How to open, edit, & convert XFDF files
A file with the XFDF file extension is an Acrobat Forms Document file that stores information usable by a PDF file, like the values in the document’s different forms. The XFDF file inserts that data directly into the PDF.
For example, if several forms in a PDF should be populated with a user’s information, it might first be taken from a database containing the user’s information and stored in the XFDF format so that the PDF file can use it.
FDF files are similar to XFDF files but use PDF syntax instead of XML formatting.
How to Open an XFDF File
If those programs aren’t helpful, try using a free text editor. If the file opens as a text document, use the text editor to read or edit the file. However, even if most of the text is illegible, you might be able to find something useful within the text that describes the format it’s in, which you can then use to find a compatible opener or editor for the file.
If the application that opens the XFDF file isn’t the program you want to use the file with, pick a different program to open the file when you double-click it.
How to Convert an XFDF File
You can’t convert an XFDF file to PDF because the two aren’t really similar in that respect. An XFDF file is used by the PDF file but can’t technically exist in the PDF format.
Also, since the XFDF file is already in the XML format, “converting” it to XML doesn’t really need to be done. If you want the file to end with the .XML file extension, just rename the .XFDF part of the file name to be .XML.
Try fdf2xfdf to convert FDF to XFDF.
To convert XFDF to some other format, you might have luck with a free file converter, but chances are that it shouldn’t really be in any other format than the one it’s already in since it’s only useful in the context of PDFs.
Creating an XFDF or FDF file from a PDF is done with Acrobat. See Adobe’s help document for the details.
Still Can’t Open the File?
If your file won’t open at this point, there’s a good chance you’re misreading the file extension. Some files use a similar file extension but that doesn’t necessarily mean that the file formats are at all similar.
XWDF is one example where it’s a VooPoo Firmware Update Data file format that, despite appearing related to XFDF files because of the similar extension, can’t be used with the programs mentioned above.