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PDF Auto Fill: Fill Form Fields by Name from JSON or CSV

PDF auto fill puts the values from a JSON or CSV file into the fields of a fillable PDF form, matched by their exact field names. The filled form stays editable, and nothing's guessed: an unknown field name stops the run with an error.

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JSON must be an object keyed by exact PDF field names. A CSV needs a field_name,value header and one data row, which fills one field.

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How to Auto Fill a PDF Form in 4 Steps

  1. 01Upload a standard AcroForm PDF.
  2. 02Upload a JSON object, or a field_name,value CSV with one row for one field.
  3. 03The tool matches values to the exact field names and checks their types.
  4. 04Download the completed interactive PDF.

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PDF Auto Fill Features and Limits

  • Exact Field MatchingValues only go into the PDF fields you name.
  • Standard AcroFormsText, checkbox, dropdown, radio and option-list fields all work.
  • Strict ValidationWrong types, options or field names get rejected, never guessed.
  • Interactive OutputThe completed PDF keeps its form fields editable.
  • Self-Hosted ProcessingNo external API, OCR, AI or third-party conversion service is involved, and uploads are deleted automatically within two hours.
  • JSON or CSVOne simple structured file per run, so the same form fills the same way every time.

PDF Auto Fill: Mapping Files, Field Types and a Real Test

PDF auto fill saves you typing when the same kind of data goes into a fillable form over and over. You upload the form and a JSON or CSV file, and every value gets written into the field with exactly that name. The filled PDF keeps its form fields, so you can still fix a value by hand.

Auto fill your PDF form now

How to auto fill a PDF form from JSON or CSV

  1. Upload a fillable PDF form (an AcroForm with real form fields).
  2. Upload a JSON or CSV mapping file whose names match the PDF's field names.
  3. Click Auto Fill and Download.
  4. The filled PDF downloads on its own, and the results screen lets you download it again.
PDF auto fill screen with form-template.pdf and auto-fill-mapping.json chosen and the Auto Fill and Download button
Our test form and its JSON mapping, ready to fill.

How field names are matched

Every key in your mapping has to be the internal name of a field in the PDF. The label printed next to a field and where it sits on the page don't matter at all.

If the mapping names a field that doesn't exist, the run stops with an error naming the unknown field. Fields your mapping doesn't mention are left as they are.

Finding the exact field names

Upload the form to Fill Out PDF Form first. It lists every field, but under a label, not the exact name: the label turns underscores into spaces and starts each word with a capital, so a field named full_name shows as Full Name.

In our October 2026 test, a mapping with the key "Full Name" was refused with the message Unknown field name: Full Name, while full_name filled the field. Treat the label as a hint. If the error names a key, try it in lower case with underscores or look the name up in a PDF editor's form editing mode.

JSON and CSV mapping files

A JSON object fills many fields

A JSON mapping is one JSON object whose names are the PDF field names. Ours looked like this: {"full_name":"Ada Lovelace","email":"ada@example.com","agree_terms":true,"country":"CA","payment":"paypal","interests":["tech","art"]}.

A CSV file fills one field

A CSV mapping has the header field_name,value and exactly one data row, so it sets one field. Whenever you need to fill several fields, use JSON. Values with commas can be quoted, as in any CSV file.

One CSV row per filled PDF does not work

A CSV with one row per person can't give you one filled PDF per row. We tried two layouts on our test form: field_name,value with two data rows, and a spreadsheet table with the columns full_name and email and one row each for two people.

Both were refused with the message CSV mapping must contain one header row and one data row, and no PDF came out. To fill the same form for lots of people, save one JSON file per person and run the tool once for each.

Supported form field types

Text fields take a string, and checkboxes take true or false. Dropdowns and radio groups take one of the options the PDF defines, spelled exactly the same way.

Option lists take an array of options in JSON, or options separated by semicolons in CSV. Every value is checked against its field type before the PDF is saved, and a wrong type or an unknown option stops the run.

What happened when we tested PDF Auto Fill

We uploaded our small test form form-template.pdf (6.9 KB, 1 page) and auto-fill-mapping.json (172 B), which sets six fields: a name, an email address, a checkbox, a dropdown, a radio group and an option list. The download, form-template_AutoFilled.pdf, was 14.2 KB and still had 1 page. Tested in October 2026.

PDF auto fill results screen with a Download button after filling form-template.pdf from auto-fill-mapping.json
The results screen after the six fields were filled.

What PDF auto fill cannot do

It works on standard AcroForm fields only. The tool uses pdf-lib, and pdf-lib does not read or fill XFA forms, so XFA-only forms can't be filled here.

A scanned or flat PDF has no fields to fill, and the tool doesn't use OCR or AI to hunt for blanks on the page. Signature fields can't be filled either.

If you'd rather type into the fields yourself, use Fill Out PDF Form. To lock the values so nobody can edit them any more, run the result through Flatten PDF.

To put a password on a completed form before sending it, use Protect PDF. If you only need some pages of a filled form, pull them into a new file with one of our page tools.

Limits and privacy

The PDF can be up to 25 MB. It's processed on our own server with no outside service, and both uploads are deleted automatically within two hours.

Frequently Asked Questions about PDF Auto Fill

Can I fill a PDF form from JSON?

Yes. Upload a fillable PDF and a JSON object whose keys match the PDF field names exactly.

Can I fill a PDF form from CSV?

Yes, one field per file. The CSV needs a field_name,value header and exactly one data row. A file with more rows is refused, so use JSON to fill several fields at once.

Does PDF auto fill support XFA or scanned forms?

No. It fills standard AcroForm fields only and doesn't run OCR.

Will the filled form stay editable?

Yes. The output isn't flattened, so every field can still be changed.

What happens when a field name or option is wrong?

The run stops with an error message. The tool never guesses, and it never puts a value into a different field.