Re: Adobe Reader DC unable to open local XFDF files, looking for help

The above is somewhat incorrect. If you set up the FDF (or XFDF) files correctly, your users won't need to do anything other than have Acrobat or Reader installed on their desktops; this won't work on mobile OSs.

In addition to the field data, your FDF will need to include a reference to the PDF and the URL to it must be fully qualified. You can then email the FDF to the user or have them download a personalized version. When they open the FDF, Acrobat/Reader launches and then  fetches the referenced PDF and essentially merges the two.

The way to think about FDF is kind of the opposite of how most people think about forms. You don't open the PDF and fill it with FDF data... though that is possible and what is outlined above. For automation tasks where you want to customize a form for an individual, you open the FDF and then slip the PDF form under it... metaphorically speaking of course.

Furthermore, I want to password-protect the PDFs from editing. Isn't importing the XFDF considered "editing" the document. I wonder if there is an API that can open a PDF, attach an XFDF to it, password protect it, and close it. I'm not talking JavaScript, but an API that is accessible by programming languages that have read/write access to the file system.

XFDF and FDF files are a special type of file that export the form field names and values or in a more advance format code between PDF files. They can be opened by text editors but cannot be opened directly by Acrobat or Adobe Reader. To open them using Acrobat, you must have opened a form that contains all or some of the form fields listed withing the XFDF or FDF file and then use Acrobat to import the XFDF, or FDF file. It is also possible to import and XFDF or FDF file using Adobe Reader if some additional JavaScript code is added to a special folder used by Adobe Reader.

If the XFDF or FDF file has a reference to a PDF file, Acrobat will try to open that file before opening the XFDF of FDF file. If Acrobat cannot open the referenced PDF file Acrobat cannot open the XFDF or FDF file.