Add your FDF file
Drop one or more .fdf files onto the converter above, or browse for them. They load into browser memory only — nothing is uploaded, so there is no size-based pricing and no server queue.
FDF to JSON
Converting a .fdf font to .json repackages the same glyphs and metrics for a different delivery target. Free, private, and validated — the file never leaves your browser.
Private for supported formats — processed in your browser
Runs on your deviceConvert supported files
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.About converting Forms Data Format to JSON data
Converting a .fdf font to .json repackages the same glyphs and metrics for a different delivery target. 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.
A .json file holds JavaScript Object Notation: nested objects, arrays, strings, numbers, booleans, and null written in a strict text syntax. It is the default data language of the web — most APIs speak nothing else. For this route the practical draw is parsers ship in the standard library of essentially every language and readable by humans and machines alike — balanced against no comments — a perpetual annoyance for configuration files, which is worth knowing before you commit a large batch.
Why convert FDF to JSON?
The practical trigger for this conversion is usually a mismatch: with .fdf, binary-ish PDF syntax makes it awkward to inspect or generate by hand. Switching to .json buys you parsers ship in the standard library of essentially every language, which is why it is the better fit for rEST and HTTP API request and response payloads. Because the conversion runs locally, trying it costs nothing but a few seconds of compute on your own machine.
FDF vs JSON at a glance
| Aspect | Forms Data Format (.fdf) | JSON data (.json) |
|---|---|---|
| Format type | Text-based — characters and structure, so there is no visual quality loss | Text-based — characters and structure, so there is no visual quality loss |
| How it stores data | 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 | exactly six value types; no dates, no comments, no trailing commas — the strictness is deliberate |
| Strongest at | extracting submitted values from a PDF form workflow | rEST and HTTP API request and response payloads |
| Weak spot | binary-ish PDF syntax makes it awkward to inspect or generate by hand | no comments — a perpetual annoyance for configuration files |
Pick JSON as the output
Select .json in the output menu next to each file. The menu only offers targets this engine can genuinely produce, so if JSON is selectable, the route is real and validated.
Convert on your device
Press Convert. The font tables are parsed and rewritten locally with fonteditor-core; glyph outlines, hinting, and kerning survive the trip.
Verify and download
Each result is signature-checked before the download unlocks, so a failed encode can never masquerade as a valid JSON file. Outputs keep the original filename with the .json extension.
FDF to JSON questions, answered
Will converting FDF to JSON lose quality?
There is no visual quality to lose — fdf is text-oriented and json is text-oriented, so the question is structural fidelity. Text, ordering, and basic structure are preserved; complex layout, embedded objects, and styling beyond the target's model are simplified.
Is it private to convert FDF files here?
Yes — the .fdf file is processed inside your browser tab and never uploaded. The font tables are parsed and rewritten locally with fonteditor-core; glyph outlines, hinting, and kerning survive the trip. Close the tab and the file is gone from memory.
Where will the JSON file work?
Browsers parse it natively through JSON.parse, every mainstream language bundles support, and most editors validate and highlight it out of the box. Viewing a raw .json file is possible in any text editor or browser tab.
Will the JSON file be bigger or smaller than my FDF?
It depends on the content: exactly six value types; no dates, no comments, no trailing commas — the strictness is deliberate. Convert one representative file first and compare before batch-processing a large set.
What happens to the metadata in my FDF file?
In .fdf, the referenced-document path is detected and deliberately omitted from the output rather than carried across. Re-encoding through the browser pipeline does not carry embedded metadata into the output, which doubles as a privacy scrub — check the exported file if you specifically need tags preserved.
Can I convert JSON back to FDF?
Yes — the reverse route exists as a separate tool. Bear in mind that round-tripping .fdf → .json → .fdf is not a perfect undo when any lossy step is involved; keep your original if fidelity matters.