*.fdd files (Form Definition Files). Form samples are binary files with the extension *.dtf. Page samples are saved in *.ptf format, a modified version of the *.fdd format.Saving and Publishing a Form; Checking a Form for Machine-Readability
Save a form
Save forms in ABBYY FormDesigner as *.fdd Form Definition Files, and save form samples as *.dtf or page samples as *.ptf with the Save As command.
To save a form, use the standard Save or Save As… command (File → Save or File → Save As…).
The Save As… command saves either a form or a form or page sample. To select a format, use the Save as type drop-down list.
Forms created in ABBYY FormDesigner are saved as