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.