Flatten PDF

How Flatten PDF works

A filled-in PDF form is still a form: the answers sit in fields on top of the page, and anyone can change them, clear them, or see them displayed differently in another app. Flattening draws each field and annotation into the page itself and removes the interactive layer, so the result looks exactly the same but is no longer editable.

Before flattening, the tool asks each form field to draw its current value, so answers typed in apps that do not save an appearance still show up. Comments, highlights, stamps and signatures that have a visible appearance are flattened the same way.

The work is done by qpdf, an open-source PDF toolkit compiled to WebAssembly, running inside this tab. Nothing is uploaded, which matters for forms that hold personal details such as tax, medical or application forms.

The flattened file keeps its name with -flattened added. Each form field is drawn with the value it holds, in the same place and at the same size, so the page looks as it did while it was a form. Flattening also helps when the same form looks different in different apps: some viewers hide field values or show them in another font, and once they are part of the page every viewer shows them alike. Several forms can be flattened at once, each with its own download button.

Flatten PDF options explained

When to use it

Flatten a form before sending it to an office that asks for a PDF they cannot alter, before printing a form that shows blank fields on some printers, before merging forms into one file, or to lock in the result after signing.

Keep an unflattened copy if you might need to change an answer later, because a flattened form cannot be filled in again.

About the PDF toolkit

Unlock, protect and flatten, and the final step of compression, use qpdf, a long-established open-source PDF toolkit that many desktop programs and servers rely on, compiled to WebAssembly so it runs in this tab. It loads the first time you use one of these tools, about 1.3 MB, and is cached. qpdf works on the internal structure of the file: it can encrypt and decrypt with the PDF standard's own methods, draw form fields into the page, and rewrite objects more compactly, all without re-rendering the pages. Because it runs on your device, passwords and the documents they protect never pass through a server, which is the point of protecting them in the first place.

Flatten PDF troubleshooting

A field looks empty after flattening

The app that filled it may not have saved the value in the field. Open the form in a browser or Acrobat, check the answer is there, save, and flatten again.

The file will not open

It is password protected. Unlock it first with Unlock PDF.

Fonts look slightly different in fields

Fields drawn fresh use a standard font where the form did not specify one. The answers are the same; only the typeface may change.

How to use Flatten PDF, step by step

1. Press "Choose PDF files" or drag PDFs onto the box.
2. Set the options if you need to; the defaults suit most uses.
3. Press "Flatten PDF". The work happens on your device.
4. Save the result with its download button.

Is it safe to do this online?

With most online tools, "online" means your file is uploaded to a company's server, processed there and kept for a while before it is deleted. Here it is not. The page downloads the tool's code to your browser, and your file is read and processed inside the tab on your own device. It is never sent to TapToConvert or anyone else.

You can check this yourself: once the page and its engine have loaded, turn off Wi-Fi and the tool still works. That also means there is no queue, no daily limit and no file size cap set by a server; the only limit is the memory your browser gives a single tab.