Add your JSON file
Drop one or more .json 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.
JSON to FDF
Restructuring .json data as .fdf changes the serialization without touching the values themselves. 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 JSON 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 JSON data to Forms Data Format
Restructuring .json data as .fdf changes the serialization without touching the values themselves. 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.
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. For this route the practical draw is far smaller than shipping a filled PDF for every response and defined inside the PDF specification rather than invented alongside it — balanced against binary-ish PDF syntax makes it awkward to inspect or generate by hand, which is worth knowing before you commit a large batch.
Why convert JSON to FDF?
The practical trigger for this conversion is usually a mismatch: with .json, no comments — a perpetual annoyance for configuration files. Switching to .fdf buys you far smaller than shipping a filled PDF for every response, which is why it is the better fit for extracting submitted values from a PDF form workflow. Because the conversion runs locally, trying it costs nothing but a few seconds of compute on your own machine.
JSON vs FDF at a glance
| Aspect | JSON data (.json) | Forms Data Format (.fdf) |
|---|---|---|
| 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 | exactly six value types; no dates, no comments, no trailing commas — the strictness is deliberate | 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 |
| Strongest at | rEST and HTTP API request and response payloads | extracting submitted values from a PDF form workflow |
| Weak spot | no comments — a perpetual annoyance for configuration files | binary-ish PDF syntax makes it awkward to inspect or generate by hand |
Pick FDF as the output
Select .fdf in the output menu next to each file. The menu only offers targets this engine can genuinely produce, so if FDF is selectable, the route is real and validated.
Convert on your device
Press Convert. The restructuring is plain local parsing — your data is never posted to a server for processing.
Verify and download
Each result is signature-checked before the download unlocks, so a failed encode can never masquerade as a valid FDF file. Outputs keep the original filename with the .fdf extension.
JSON to FDF questions, answered
Will converting JSON to FDF lose quality?
There is no visual quality to lose — json is text-oriented and fdf 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 JSON files here?
Yes — the .json file is processed inside your browser tab and never uploaded. The restructuring is plain local parsing — your data is never posted to a server for processing. Close the tab and the file is gone from memory.
Where will the FDF file work?
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.
Will the FDF file be bigger or smaller than my JSON?
It depends on the content: 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. Convert one representative file first and compare before batch-processing a large set.
Can I convert FDF back to JSON?
Yes — the reverse route exists as a separate tool. Bear in mind that round-tripping .json → .fdf → .json is not a perfect undo when any lossy step is involved; keep your original if fidelity matters.