How filling a PDF form works
A fillable PDF contains real form fields: text boxes, checkboxes, round radio buttons and dropdown lists, each with a name and a position on the page. Government departments, banks, schools and employers publish forms this way so you can type instead of printing and handwriting.
This tool reads those fields with pdf-lib, draws each page with PDF.js, and places a matching input exactly over every field. You type, tick and choose on what looks like the paper form. When you save, your answers are written back into the PDF’s own fields, so the result behaves like a form filled in Adobe Reader.
Step by step
- Choose the PDF form. The tool counts the fields it finds.
- Fill in the blue boxes. Text boxes take typing, checkboxes take a click, and radio buttons let you pick one option of a group. Dropdowns open a list. Press Tab to jump to the next field.
- Small boxes on a phone? Switch to As a list to see every field as a large, labelled input. Both views edit the same answers.
- Decide about flattening (see below).
- Save and download. The file name ends in “-filled” so your blank original is kept.
Should you flatten the form?
| Choose | When | What you get |
|---|---|---|
| Keep fields (default) | You may need to change answers later, or someone else will add theirs | Answers stay editable in any PDF reader |
| Flatten | You are submitting a final copy | Answers become part of the page; nobody can change them by accident |
Flattening also fixes a common problem: some portals and older printers ignore form fields and show a blank form. A flattened copy always shows your answers. If you only need to flatten a form you already filled elsewhere, Flatten PDF does exactly that.
A worked example
You download a 3-page rental application with 42 fields. You fill in your name, address and phone number, tick “Employed full-time”, choose “2 adults” from a dropdown, and leave the guarantor section empty. The tool warns that “Applicant signature date” is required and still empty. You fill it, tick Flatten, and save.
Next, you open the saved file in Sign PDF to add your signature on page 3. Finally, Compress PDF shrinks it under the agent’s 2 MB email limit. Every step happens on your own device.
Tips
- Character limits: some boxes accept only a set number of characters (a postcode or a national ID number). The tool stops you at the limit, just like Adobe Reader.
- Read-only fields are shown but cannot be changed. The form’s author locked them.
- Answers in other scripts: names in Arabic, Urdu, Cyrillic or Chinese are kept in the field, and PDF readers draw them with a suitable font. Flattening such answers is blocked, because the built-in PDF font cannot draw those letters. Keep the fields editable instead.
- No fields found? The PDF is “flat”: a picture or plain text of a form. Use Edit PDF and its Text tool to type answers where they belong.
Compared with typical online form fillers
| This tool | Typical online form fillers | |
|---|---|---|
| Your form leaves your device | No | Yes, uploaded to a server |
| Account needed | No | Often, to download or save |
| Free limits | None | Often a few documents per month |
| Flatten option | Yes | Sometimes paid |
| Works offline after loading | Yes | No |
Forms are often the most personal documents people handle: tax returns, passport and visa applications, medical histories and bank forms. That is the strongest reason to fill them on your own device.
Limits
- Pure XFA forms, which open with a message like “Please wait… If this message is not eventually replaced”, only work in Adobe Reader. Many hybrid forms also contain standard fields; those are filled here and the XFA layer is removed when you save.
- Calculated fields (totals that add themselves up) are not recalculated. Type the total yourself.
- Signature fields are not filled here. Add a signature image with Sign PDF.