>Thanks for the idea William, do you know if the key also exits when only Acrobat Reader is installed?
>
>>A correction: easier (and I think, more correct) than using the sub-key, use the default value there:
>>Read the registry key at: \\HKEY_Classes_root\.xfdf : finds default value "AcroExch.XFDFDoc"

I believe that it does exist with only Acrobat Reader. I remember exploring the FDF file format, and finding references to the PDF Form Toolkit being necessary on the Adobe website, but I think they were old documents that only related to previous versions of Acrobat... the current version seems to include just about everything that doesn't have to do with changing a PDF.