PDF Forms for Filling and Exporting Data
How to export, fill or lock the fields of an existing PDF form
Export PDF form fields as JSON, fill them with values, or reset, lock, unlock or remove selected fields. Review the field names before supplying data, because a visible label may differ from the internal name. Open the result in a PDF reader to check text, checkboxes and field behavior. This works with form fields already present in the document.
Cost: Free to use. File size and usage limits apply.
How to work with a PDF form
Upload one PDF form
Click Choose PDF or pick a file from Uploads. The tool takes one PDF of up to 200 MB and scans it right away. The settings panel then shows how many fillable fields it found.
Choose an action
Action starts on Export form data, which needs no further input. Switch to Fill form to type values, or to Lock fields, Unlock fields, Reset fields or Remove fields to change the fields themselves.
Enter values or field names
For Fill form, edit the field cards below the settings. For the other four actions, type the fields you want to change into Field names (optional).
Apply the action
Click Apply form action. When you fill a form, the tool reads the finished PDF back and confirms that every value was stored.
Download the result
Click Download result to save the JSON file or the updated PDF. The result is also stored in the shared file manager. For another PDF step, select the updated PDF from Uploads, for example to fill a form you just unlocked.
What each action does
Export form data
Saves every field as a JSON file: type, name, ID, page, current value, options and locked state. The PDF is not changed. Use it to read the answers in a filled form or as a template for Advanced JSON.
Fill form
Writes your values into the existing fields and returns a PDF. The fields stay interactive, so the recipient can still edit them unless you lock them afterwards.
Lock fields
Makes fields read-only. PDF viewers that honor the flag show the values without accepting ordinary edits. Leave the names empty to lock the whole form, for example after filling it.
Unlock fields
Makes read-only fields editable again. Run it first when a form arrives with locked fields you need to change, because Fill form keeps locked values as they are.
Reset fields
Sets fields back to the default value the form author defined, which is empty for most fields. It also works on locked fields. Leave the names empty to clear the whole form.
Remove fields
Deletes the named fields from the form. Text and lines printed on the page stay. This action needs at least one field name.
Settings
- Action
- Six choices, default Export form data. Fill form adds Fill mode. Lock fields, Unlock fields, Reset fields and Remove fields add Field names (optional).
- Fill mode: Form fields
- The default. Shows one card per field with its label, its internal name, its ID, the page and a Required, Optional or Requirement not reported badge. Each card starts with the value the PDF already contains. Required fields must be filled before you can apply. Locked fields are greyed out with a Locked badge.
- Fill mode: Advanced JSON
- Lets you edit all values as text in Form data (JSON). Useful for long forms, or when you prepared the values elsewhere from an earlier export.
- Form data (JSON)
- Pre-filled with this PDF's exported structure as soon as the scan finishes. Change only the values. The rules are in the JSON section below.
- Field names (optional)
- Separate names or numeric IDs with commas or line breaks. Spaces around an entry are ignored. Leave the box empty to lock, unlock or reset every field. Remove fields requires at least one entry. Use the internal name exactly as written, including upper and lower case, or the field's numeric ID. To look them up, switch Action to Fill form: each card shows the name under the label and the ID next to the page number.
How each field type is filled
In Form fields mode each card uses a control that matches the field type in the PDF. Options always come from the PDF itself.
- Text field
- A single-line box, or a larger box for multi-line fields. If the form sets a maximum length, typing stops there and a counter such as
12/80 charactersshows how much you have used. - Date field
- A text box whose placeholder shows the format the form expects, for example
dd.mm.yyyy. The text is stored exactly as you type it, so follow that format. - Checkbox
- Tick or untick the box. The text next to it reads Checked or Unchecked.
- Radio button group
- Pick one of the options the form defines.
- Combo box
- A drop-down with the form's options and No selection. If the form author allowed custom entries, you get a text box instead, with the options offered as suggestions.
- List box
- A drop-down for lists that allow one choice, or a set of checkboxes for lists that allow several.
The form JSON format
Export form data writes the form structure of the pdfcpu PDF library. A header block records the source file and the pdfcpu version. The forms array groups fields by type: textfield, datefield, checkbox, radiobuttongroup, combobox and listbox. Each field lists pages, id, name, usually altname (the label you see as a tooltip), its value and locked, plus type details such as maxlen, format, options or multi.
Values are text, with two exceptions: checkboxes use true or false, and list boxes use a values array. For radio groups and combo boxes without custom entries, the value must be one of the listed options or empty.
In Advanced JSON, change only value, or values for list boxes. Every other property must stay exactly as exported, and the number of forms must match. That is why JSON from a different PDF, or a simple map such as {"full_name": "Ada"}, is rejected. You can paste the file from Export form data of the same PDF unchanged, and you can delete field entries you want to leave untouched.
Formats and limits
- Input format
- PDF with interactive form fields
- Output format
- Export form data: one JSON file. All other actions: one PDF.
- Maximum file size
- 200 MB
- Files per job
- 1 PDF
- Field types
- Text, date, checkbox, radio button group, combo box and list box
- Password-protected PDFs
- PDFs that open without a password but restrict editing are processed, and the result keeps that protection. PDFs that ask for a password when opened need Unlock PDF first.
- Processing
- On our servers with the pdfcpu PDF library. No AI service is involved. A job can run for up to 15 minutes.
- Watermark
- None
- Storage
- Uploads and results are deleted automatically after 48 hours for guests and after 30 days for free accounts. Paid plans can keep files longer.
Frequently asked questions
Why does the tool say my PDF has no fillable form fields?
The file has no interactive fields. Boxes and lines printed on the page only look like a form, and the fill-and-sign feature of many viewers places free text on top of the page instead of filling fields. PDF Info shows Form: No for such files. A form stored only in the older XML-based XFA format also has no standard fields for this tool to read.
Why did Lock, Reset or Remove end with an error?
Check the entries in Field names (optional) against the names and IDs shown in Fill form. Each entry must match an internal field name exactly, including upper and lower case, or a numeric ID. A field's visible label may be different from its name. Separate entries with commas or line breaks, and include at least one for Remove fields.
Why can't I change some fields in Form fields mode?
They are read-only in the PDF and show a Locked badge. Run Unlock fields first, then select the unlocked PDF in Uploads and fill it. If every field is locked, the tool reports that the PDF has no editable form fields.
Does locking protect the values I filled in?
Locking sets each field's read-only flag. Check the result in the recipient's viewer, since behavior depends on the software. Anyone with a PDF editor, or Unlock fields here, can clear the flag again. The values also stay form data rather than becoming part of the page. To restrict editing, lock the fields and then set permissions with PDF Permissions.
Why is Apply form action greyed out?
Either no PDF is selected, or Fill form is active and the field scan is still running. In Form fields mode the button also waits until the preview has read which fields are required. If the panel shows Form fields unavailable, click Retry.