A Forms Data Format (FDF) file is a formatted ASCII file which contains key:value pairs defining the ﬁeld names and associated values that are used to populate a form. Forms Data Format (FDF) is defined in the international stand for Portable Document Format; ISO-32000. See ISO-32000-1:2008 Section 12.7.7.
Following is an example of a simple FDF file:
1 0 obj
<< /Fields [
<< /T (ﬁeld-name-1) /V (value of ﬁeld-name-1) >>
<< /T (ﬁeld-name-2) /V (value of ﬁeld-name-2) >>
<< /Root 1 0 R >>
FDF is associated with Acrobat Forms (AcroForms) and were introduced in PDF Version 1.2.