How to Serve FDF to Fill Forms?

One way to automatically fill an online PDF form is to serve a data-packed FDF file (with MIME type application/vnd.fdf). The user's browser will open Acrobat/Reader and pass it the FDF data. Acrobat/Reader will read the FDF data to locate the PDF form. It will load and display this PDF and then populate its fields from the FDF. The PDF form in question should be available from your web server and the FDF data should reference it by URL using the /F key, as we do in our preceding example.

Check your web server to make sure it sends the appropriate Content-type: application/vnd.fdf header when serving FDF files. Or, send the header directly from your script.

This technique is simple, but it has limitations. First, not all browsers know how to handle FDF data. Second, this technique does not always work inside of HTML frames. The next technique overcomes both of these problems.