Flatten PDF Files

When do you need to flatten a PDF?

When you've filled in an interactive PDF form (a scholarship application, a university registration form, an administrative request) and want to send it so nobody can change your answers just by clicking a field. Or when another program shows the fields empty even though you filled them, because some viewers and upload portals don't display interactive field values. Flattening makes the field contents a fixed part of the page.

What the tool does exactly

The "Flattening Mode" menu offers two methods:

• Flatten Form Fields & Signatures Only (default): every interactive field (text box, checkbox, dropdown) is drawn onto the page with its current value, and the field itself is removed. The rest of the page is untouched: text stays selectable, quality doesn't change, and the size stays close to the original.
• Full Visual Rasterization: each page is rendered with PDF.js at double resolution and saved as a JPEG image in a new file. Nothing stays editable or selectable, but the text becomes a picture and the file usually gets larger.

Note: the first method handles form fields only. Comments, sticky notes and highlights added in a PDF viewer are not merged into the page this way.

How to flatten a PDF

1. 1
   Choose a PDF or drag it onto the upload box.
2. 2
   Under "Flattening Mode", pick "Flatten Form Fields & Signatures Only" or "Full Visual Rasterization".
3. 3
   Click "Flatten & Lock PDF Now".
4. 4
   Use "Preview Result" to check your answers are visible, then "Download Result". The file keeps its name with _flattened added.

Which mode should you choose?

For ordinary forms, use the first mode: a clean, light result that keeps real text. Full rasterization helps when you want the document to be a completely fixed image, but it isn't real protection: someone determined can still retype the page. For actual protection, add a password with Protect PDF. If the file grows after full rasterization, try Compress PDF.

Limitations

• One file at a time.
• The first mode doesn't merge comments or annotations, only form fields.
• In our test with a ticked checkbox, the full mode produced an empty box while the form-fields mode kept the tick. Always check the preview.
• A file signed with a digital certificate loses signature validity after any change, and flattening is a change.
• A file with a password or permission restrictions (no printing or editing) isn't processed: a message asks you to open it first with Unlock PDF and try again with the unlocked copy.
• There's no undo inside the output file, so keep the original if you may need to edit the form again.

Where is the processing done?

Both methods run on your own device, inside the browser tab, using pdf-lib and PDF.js. The file never passes through a server of ours.

Flatten PDF: frequently asked questions