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Fill PDF Form Online Free — Auto-Detect Fields | Synthixx Tools

Fills in a PDF that has interactive form fields, or, if it has none, lets you place typed text at chosen positions on any page. Filled forms are flattened, so the values become fixed page content.

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Upload a PDF to start filling or adding text

Fill PDF forms or add text:

Interactive forms → auto-detect and fill fields
Static PDFs → add text anywhere on the page
Choose position and font size for text
100% free, private, no signup

How to Use

1Drop a PDF onto the upload area, or click to choose one.
2If form fields are detected, a list appears: type into text fields, tick checkboxes, and choose from dropdowns.
3If no fields are found, click + Add Text, then enter the text, the X and Y position, font size and page number.
4Click Fill PDF Form (or Add Text to PDF for a flat file).
5Download filled.pdf.

About this tool

Updated September 19, 2026

Two modes: real form fields or placed text

The tool checks your PDF for interactive form fields. If it finds them, you fill them from a list; if not, you add typed text at coordinates you choose.

In form mode it lists each field with its name and type, and supports text fields, checkboxes, dropdowns and radio groups. After your values are applied, the form is flattened, so the answers become fixed content. In text mode you press + Add Text and set the text, X and Y position (in points from the top-left), font size and page number. Text is drawn in black Helvetica. Output is saved as filled.pdf, one PDF at a time. You can add several text entries, each with its own page number, and remove any entry before you run the tool.

When it works well

It suits standard fillable forms and quick additions to flat documents, but not layout-precise editing.

• An application form with fillable fields: type the answers, then send the flattened copy. • A form with no fields where you only need a name, date or short note added at a known position. If you only want to lock in fields that are already filled, Flatten PDF does just that. To combine the filled form with other documents afterwards, use Merge PDF.

Limits to expect

No visual preview, Latin-only text, and flattening cannot be undone.

Positioning free text takes some trial and error because you cannot click on the page; adjust the X and Y numbers and check the output. If a page number is higher than the page count, the text goes on the first page. Flattening is applied whenever at least one form field was filled, and cannot be reversed, so keep the blank original. Some unusual forms cannot be flattened, in which case fields stay editable. Fonts outside basic Latin are not supported, and the tool does not create signatures. Everything happens in your browser; the file is not uploaded.

Features

Detects interactive AcroForm fields and lists them by name and type
Supports text fields, checkboxes, dropdowns and radio groups
For PDFs without fields: add text boxes with X, Y, font size and page number
Text is drawn in black Helvetica
Form mode flattens the form once a field has been filled, so values are no longer editable
One PDF per run, up to 200 MB
Runs in your browser; the file is not uploaded

FAQ

Can I type directly on the page preview?

No. There is no page preview. Detected form fields are filled from a list, and text on flat PDFs is placed by entering X and Y coordinates in PDF points measured from the top-left.

Can I edit the form again afterwards?

Probably not. After filling, the tool flattens the form, which turns the fields into ordinary page content. Keep the original if you need an editable copy.

Why can I not add free text to a PDF that has form fields?

The tool picks one mode automatically: form fields if any exist, otherwise free text. A form PDF will only use form mode.

Does it support non-English text?

Free text uses the standard Helvetica font, which covers basic Latin characters only. Characters outside that set may cause an error or fail to appear.

Does it add a signature?

No. It only enters text or form values. It does not create digital signatures.

Are my files uploaded?

No. The PDF is processed in your browser.

Flatten PDF

Turn fillable PDF form fields into fixed page content that can no longer be edited.

Sign PDF

Stamp a typed name on the last page of a PDF at one of six preset positions.

Merge PDF

Combine several PDF files into one merged.pdf, in the order you arrange them.