PDF Form Filler

Open a PDF that has form fields (an AcroForm, the kind Acrobat calls "fillable") and every page is shown with its fields sitting on top as real inputs. Type, tick, choose, then click Download filled PDF.

Which fields become editable. Text fields become a text box, or a text area when the field is marked multi-line, and a maximum length set in the PDF is enforced as you type. Checkboxes and radio buttons become native toggles; radio buttons that share a field name act as one group, so picking one clears the others. Dropdowns and list boxes become a select, with multiple selection when the PDF allows it. Read-only fields are shown but locked. Signature fields and push buttons are left as they are.

How the file is written. Reading and saving both go through pdf.js, the PDF engine inside Firefox. The page is rendered without its form widgets, the HTML inputs are placed on the widget rectangles, and on download the values go into pdf.js's annotation storage and are saved back into the same file with fresh appearance streams, so the text shows up in Acrobat, Preview, Chrome and on print. The output is still a fillable form: open it again here or in any reader and the fields are still editable.

Text that does not fit. A PDF field has a fixed box and usually a fixed font size, so a long address gets cut off on paper. Every text field is drawn at the size it will print at, and a field whose text will not fit gets a red border, with a count in the toolbar. Click a field to set its size in points (leave it empty for the reader's automatic size), or click Shrink text to fit to set each red field to the largest size, in half-point steps, at which its text fits: one line for a single-line field, word-wrapped lines for a multi-line one. The new size is written into the field itself, so it also applies when the file is opened in another reader.

Flatten. Tick Flatten before downloading and the values are burned into the page content, the form fields removed. Use it for a copy you send and do not want changed. This step runs through pdf-lib and keeps the appearance pdf.js already drew, so accented and non-Latin text survives. It cannot be undone, so keep the unflattened copy if you might need to edit again.

What it cannot fill. A scanned form, or a form printed to PDF, has no fields: it is a picture of boxes, and the tool says so. Dynamic XFA forms (built with Adobe LiveCycle, still used by some public administrations) render their fields at open time with scripting only Adobe Reader runs. Hybrid forms that carry both XFA and AcroForm fields do work.

Privacy. The PDF is read with the File API and processed in this browser tab. Tax forms, application forms and contracts never leave your device, and DevTools → Network shows no request carrying the file. To merge the result with other PDFs or remove pages, use PDF Toolkit.