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Data format

FDF converter

An .fdf file holds the data from a PDF form without the form itself: field names and their values, stored in PDF's own object syntax, so the values can travel separately from the document and be merged back into it later.

Private for supported formats — processed in your browser

Convert supported files

Runs on your device

Drop FDF files here

Batch files can each use a different output. Nothing uploads for local conversions.

Working inputs include camera RAW, browser-local audio/video, PDF, CBZ/CBR comics, office documents, ebooks, markup, 3D models, structured text, images, and archives.

Where FDF comes from

Adobe introduced FDF with Acrobat in the mid-1990s so a filled form could be submitted as a small data file rather than a whole PDF. It is defined in the PDF specification itself, which is why an FDF file is structurally a PDF — header, indirect objects, xref table, trailer — carrying an /FDF dictionary instead of pages. Adobe later added the XML-based XFDF, and most modern workflows prefer it, but FDF remains what many older form pipelines emit.

How FDF works

  • The file begins with %FDF-1.x and is otherwise a normal PDF object graph, so it needs a real PDF parser rather than a text scan.
  • The /Fields array holds dictionaries with /T (the field name) and /V (the value), and fields may nest to form dotted names.
  • An /F entry points at the PDF the data belongs to — often an absolute path from the machine that filled the form, which is a quiet privacy leak.
  • FDF can carry actions such as /SubmitForm and /Launch, which is why it must never be processed permissively.
  • String values use PDF string syntax, so parentheses and backslashes inside a value have to be escaped.

When to use FDF

  • Extracting submitted values from a PDF form workflow
  • Migrating legacy form data to XFDF or JSON
  • Auditing what a filled form actually contains without opening the PDF
  • Merging archived responses back into a blank form

Strengths and limitations

Strengths

  • Far smaller than shipping a filled PDF for every response
  • Defined inside the PDF specification rather than invented alongside it
  • Round-trips cleanly with Acrobat and the tools built on it

Limitations

  • Binary-ish PDF syntax makes it awkward to inspect or generate by hand
  • Document references can embed local filesystem paths
  • Superseded by XFDF in most current tooling

Compatibility

Adobe Acrobat, pdftk, iText and PDF form engines read FDF. Novus Convert parses it locally with a real PDF cursor and converts to XFDF and JSON. Files containing /URI, /Launch, /SubmitForm or /GoToR actions are refused rather than parsed, and any document reference is reported as omitted instead of being followed.

The referenced-document path is detected and deliberately omitted from the output rather than carried across.

Convert FDF to another format

Convert other formats to FDF