Comparing signed PDF documents

Each time a person digitally signs a PDF document that already has one signature, Acrobat saves the changes and signature of each subsequent signatory in a special appended version of the file. You can then compare the various versions to note what changes, if any, each signatory made.
Acrobat notes when a PDF document that you’ve sent out for subsequent signatures comes back to you with changes by adding a Document Was Modified item to the Signatures palette. You can then display the details of the modifications by clicking the Expand button (with the plus sign on Windows and the triangle pointing to the right on the Mac). Note that the detailed change items shown in the expanded list are purely informational and do not perform as bookmarks.
To have Acrobat do a side-by-side comparison of the versions to let you visually compare the changes, select View Signed Version on the Signatures palette Options pop-up menu. Acrobat then displays the original version of the PDF file and the most current version in a Document pane. To compare the files side by side, choose Window➪Tile➪Vertically. You can then scroll through the pages, visually noting the differences. When you’re finished checking the changes, close the original version on the left by clicking its document window’s Close button and maximize the latest version on the right by clicking its document window’s Maximize button. If you would prefer, you can have Acrobat do a page-by-page comparison and locate all the changes between the latest signed version and the original. To do this, select Compare Signed Version to Current Document on the Signatures palette Options pop-up menu. Acrobat then performs a page-by-page comparison and creates a second PDF document containing only the pages that have changed. These changed pages are displayed side by side. When you have finished comparing these pages, you can close this newly created document by pressing Ctrl+W (Ô+W). You can then save it in its own PDF file by clicking the Yes button in the alert dialog box that asks you if you want to save the changes before closing. If you have no further need for this comparison PDF file, you can click the No button to abandon the comparison document and just return to the most up-to-date signed version of the PDF document.

Adding certificates to your Trusted Certificates list

The way that you add the certificates that you receive to your Trusted Certificates list depends upon how you receive them. If you receive an e-mail message with a certificate attached, you can launch Acrobat, validate the certificate, and add the certificate to your Trusted Certificates list all by simply opening the certificate file attached to the message in your e-mail program (in most programs, you open an attachment by double-clicking the file attachment icon).
When Acrobat launches, it displays the Data Exchange File - Import Contact dialog box. To add the certificate to your list, click the Set Contact Trust button to open the Import Contact Settings dialog box. The Trust Signatures Created with this Certificate check box is selected by default. Click the Import button to import the certificate data and create a Digital ID certificate that will appear in your Trusted Identities list. If you have access to someone’s Self-Sign Security certificate file on your computer system, you can add it to your Trusted Certificates list by clicking the Import from File button in the Trusted Certificates portion of your User Settings dialog box. To do this, follow these steps:

1. Choose Advanced➪Manage Digital IDs➪Trusted Identities to open the Manage Trusted Identities dialog box.
2. Click the Add Contacts button to open the Select Contacts to Add dialog box, and then click the Browse for Certificates button.
3. Locate the certificate exchange file you want to import in the LocateCertificate File dialog box, and then click the Open button. The selected certificate data file appears in the upper list box of the Select Contacts to Add dialog box.
4. Click the Add to Contacts List button to display the certificate exchange file in the Contacts to Add list box below; then click OK.
5. Click OK to close the alert dialog box and return to your Manage Trusted Identities dialog box, where you see the name of the person you just added to your Trusted Identities list.
6. Click the Close button to close the Manage Trusted Identities dialog box.

Exchanging certificates with associates

You can simplify the process of validating signatures in the PDF files you review by having all the review team members exchange copies of their Self-Sign Security certificates. Acrobat makes this easy by adding an export function to the Manage Trusted Identities dialog box. To open this dialog box, choose Advanced➪Manage Digital IDs➪Trusted Identities. Select your Digital ID from the list box in the Manage Trusted Identities dialog box and click the Export button to open the Data Exchange File - Export Options dialog box. Two radio buttons appear in the Export options section. The first is the E-mail the Data to Someone radio button that you can select to send a copy of your certificate to team members in a new e-mail message. The second is the Save the Data to File radio button that you can use to make a copy of the certificate file that others can import into their Trusted Certificates list. (For example, you can use this option if you and your coworkers are on the same network and share access to certain folders.)
When you select the Save the Data to a File radio button, Acrobat opens an Export Data As dialog box, where you can designate the drive and folder on which the copy of your certificate is saved (saved in a special Acrobat Self-Sign key file format that uses a .fdf file extension) when you click the Save button. When you select the E-mail the Data to Someone radio button, Acrobat opens the Compose E-mail dialog box, To send the e-mail, fill in the recipient’s e-mail address in the To text box, make any necessary changes in the default text provided in the message window, and click the E-mail button. Acrobat transfers the information into your e-mail client in order to send your certificate data to someone else.

Validating PDF digital signatures

Whenever you add your own signature to a PDF document, Acrobat automatically uses your user Digital ID information to verify your signature as valid (indicated by the green check mark and the text Signature Valid underneath it). When you receive a document that has been signed by other people, their signatures will not automatically be recognized as valid when you open the PDF file.
You can then validate their signatures. As part of this process, you need to get in contact with the signatory and verify that one or both of the two socalled fingerprint numbers stored in the public key attached to the signature in your PDF document match the fingerprint numbers in the signatory’s public key stored as part of his or her certificate attributes on his or her hard drive. (The two fingerprints are made up of a combination of letters and numbers that make your software serial number look short; the first is called the MD5 Fingerprint, and the second is called the SHA-1 Fingerprint.) To validate a signature in a PDF document that you have open, follow these steps:

1. Open the Signatures palette and select the name of the unknown signatory you want to validate (indicated by a blue question mark before the name), and then select Validate Signature on the Signature palette Options pop-up menu.
2. If the unknown signatory has not been added to your list of trusted certificates, Acrobat next displays the Signature Validation Status dialog box.
3. Click the Signature Properties button. The Signature Properties dialog box appears.
4. Use the contact information (if listed) to get a hold of the signatory (preferably by telephone) to verify the MD5 and/or the SHA-1 Fingerprint numbers listed at the bottom of the Certificate Attributes dialog box. Click the Show Certificate button to view these numbers. To find these numbers to read off to you, the signatory must choose Advanced➪Manage Digital IDs➪My Digital ID, select their Digital ID in the Manage My Digital IDs dialog box, and click the Settings button to open the Set Digital ID Usage dialog box. The signatory then clicks the Show Certificate Details button to open the Certificate Attributes dialog box and view their MD5 and SHA-1 Fingerprint numbers.
5. If the fingerprint numbers on your screen match the numbers given to you over the phone, click the Trust Identity button. The Certificate Security-Alert dialog box opens, telling you that Trusting Certificates directly from a document is unwise.
6. Click OK to close the Alert box and open the Import Contact Settings dialog box.
7. Click the Import button and then click OK in the Import Complete dialog box to add the person to your list of trusted certificates and to validate the selected signature in the PDF document.

You can quickly validate individual signatures for the people you’ve added to your Trusted Certificates list by simply double-clicking their signature fields. Acrobat will quickly search your list and, upon finding the person’s certificate, display a Signature Validation Status alert dialog box, informing you that the signature is valid. You can also use this technique on your own signatures in the event that they show up as unknown signatures when you reopen the PDF document, even when your Digital ID file is open. To update all the signatures in your PDF at one time, simply choose Document➪Digital Signatures➪ Validate All Signatures in Document, or select the Validate All Signatures in Document option on the Signatures palette Options pop-up menu.

Signing a PDF document using a predefined signature field

You can also digitally sign a PDF document by using a signature form field that’s already been added to it. To sign a document in a predefined signature form field, you follow these steps:

1. Open your Digital ID file by choosing Advanced➪Manage Digital IDs➪My Digital ID Files➪Select My Digital ID File. The Select My Digital ID File dialog box opens.
2. Select the filename of your user Digital ID in the Digital ID File dropdown list, enter your password in User Password text box, and click the OK button.
3. If the Signatures palette isn’t open and selected in the Navigation pane, choose View➪Navigation Tabs➪Signatures.
4. Click the name of the signature field you want to sign in the Signatures palette to highlight it, and then select Sign Signature Field on the Signatures palette Options pop-up menu to open the Apply Signature to Document dialog box.
5. Enter your user Digital ID password in the Confirm Password text box if necessary, and then modify the settings in the other options (Reason for Signing, Location, Your Contact Information, and Signature Appearance) as desired. Refer to Steps 5 through 10 in preceding post, “Adding a visible or invisible signature to a PDF document,” for details.
6. Click the Sign and Save button to save your changes and signature in the selected signature field in its current location with the same filename.

Alternatively, click the Sign and Save As button to open the Save As dialog box, where you can modify the file’s location and/or save it under a new filename.
As with the other methods of digitally signing a PDF document, after Acrobat finishes saving the signed document, the program displays an alert dialog box, informing that you have successfully signed it. As soon as you click the OK button to close the alert dialog box, you can see your signature in the signature form field. Figure shows you a PDF document after I signed a signature form field beneath the book title and byline.

Adding a visible or invisible signature to a PDF document

When signing a document, you can sign it invisibly so that no signature form field appears in the PDF document, or you can sign it so that all your signature information appears (as designated in the Configure Signature Appearance dialog box), including any graphic that you’ve selected.
To sign a document, take these steps:

1. Open your Digital ID file by choosing Advanced➪Manage Digital IDs➪My Digital ID Files➪Select My Digital ID File.The Select My Digital ID File dialog box opens.
2. Select the filename of your user Digital ID in the Digital ID File dropdown list, enter your password in User Password text box, and click the OK button.
3. Choose Document➪Digital Signatures➪Sign this Document or, if the Sign Task button is open on the Tasks toolbar, click it and choose Sign This Document on the pop-up menu. If the Alert - Document Is Not Certified dialog box appears, you are given the opportunity to add a Certifying Signature to the document, which will be invalidated if unauthorized changes are made. To specify this added security feature, click the Certify Document button and follow the prompts; otherwise, click the Continue Signing button to open the Sign Document dialog box.
4. Select the Create a New Invisible Signature radio button, and then click Next to open the Apply Signature to Document dialog box. Alternatively, if you wish to sign the PDF document with a visible signature, select the Create a New Signature Field to Sign radio button, click Next, and then draw a signature field in the PDF document by dragging the mouse in the area you want to sign.
5. If you want to add the reason for signing the document, your location, or contact information to the signature information (that can be viewed in the Signatures palette), click the Show Options button to expand the Apply Signature to Document dialog box.
6. To include the reason for signing the document as part of the signature information, select the reason from the Reason for Signing Document drop-down list (such as I Am Approving This Document or I Am the Author of This Document). Note that you can edit the reason you select by clicking the insertion point in the text and then inserting or deleting text as needed.
7. If you wish to save your location as part of the digital signature information, click in the Location text box and enter your current location (as in Chicago or Corporate Headquarters).
8. If you wish to include contact information, such as your telephone number, so that coworkers can contact you if they need your certificate in order to verify your digital signature, click in the Your Contact Information text box and enter that information there.
9. If you’re using a visible signature, by default, Acrobat selects Standard Text as the Signature Appearance. To preview how this signature field will appear in the document, click the Preview button. If you wish to select a new appearance for your signature field, select its name in the Signature Appearance drop-down list. To create a new signature appearance, click the New button. To edit the appearance you selected in the drop-down list, click the Edit button, which replaces the Preview button when you select an appearance you created.
   
10. Click the Sign and Save button to save your changes and signature in the document in its current location with the same filename. Alternatively, click the Sign and Save As button to open the Save As dialog box, where you can modify the file’s location and/or save it under a new filename. After you click the Sign and Save button in the Apply Signature to Document dialog box (to save the file with the same name) or the Save button in the Save As dialog box (to save the file in a new location or with a new filename), Acrobat saves the PDF document with your signature and then displays a Certificate Security - Alert dialog box, informing you that you have successfully signed the document.

After you click OK to close this dialog box, you can verify that you’ve signed the document (if you used an invisible signature) by opening the Signatures palette by clicking the Signatures tab on the Navigation pane (if the palette isn’t already displayed in the Navigation pane). To display the detailed information you added to your signature (including the reason, location, and contact information), click the Expand button (the plus sign on Windows and the triangle pointing right on the Mac) to expand the signature information. If you used a visible signature to sign the document, after you click OK to close the alert dialog box, you can see your signature right on the document page. Note that the Signatures palette shown in this figure displays a list of the detailed signature information that also appears (much smaller) in the signature field to the right of the facsimile of my handwritten signature. You can always review the signatory information for a particular signature in its Signature Properties dialog box. You can open this dialog box for a visible signature by right-clicking (Control+clicking on the Mac) the signature field and then clicking Properties on the context menu. You can also open this dialog box (for an invisible or visible signature) by selecting the signatory’s name in the Signatures palette and then selecting Properties at the bottom of the Options pop-up menu.

Signing a PDF document

After you’ve set up your Digital ID, you’re ready to use it to digitally sign off on PDF documents. In digitally signing a PDF document, you add a special signature form field to the document that contains the mark and signing information that you want displayed. The first time a document is signed by you or one of your coworkers, Acrobat saves the PDF file with the signature in a special append-only form. Every time someone digitally signs the document after that, Acrobat saves a new version of the file to which his or her editing changes and signature are appended.
Keep in mind that when you’re viewing a PDF document with multiple signatures, you’re looking at the latest version of the document with all changes since the first time it was signed. If you want, you can view the original version of the signed document side by side with the most current version by selecting the signatory in the Signatures palette and then selecting View Signed Version in the Options pop-up menu. You can also compare the changes between the original signed version and the current document (by selecting Compare Signed Version to Current Version on the same Signatures palette Options pop-up menu).
If you ever decide that you should manually save a PDF document that’s been digitally signed, don’t use the File➪Save command to do it. Use instead the File➪Save As command to save a copy of the PDF document under a new filename. If you use File➪Save to save a signed PDF document, you automatically invalidate all the signatures in it.