What flattening a form actually does
A fillable PDF keeps each answer in a form field that sits on top of the page. The field has a name, a value and a look, and any PDF viewer can change the value. Flattening draws each field's current look into the page itself and then removes the field.
- Answers can't be retyped in an ordinary PDF viewer.
- Tick boxes stay ticked and drop-down lists stop being lists.
- The form looks the same everywhere. Unflattened fields can show blank, or show the wrong font, in some phone apps, browser previews and print drivers.
- Comments, highlights and stamps on the page are drawn in at the same time.
The text you typed is still real text after flattening, so it can be searched and copied. Only the boxes go.
When to flatten a form, and when not to
Flatten it:
- before you send a completed form back - an application, a timesheet, a variation sheet, a site checklist - so the other person sees exactly what you saw;
- before you put several filled copies of the same form into one PDF. Fields with the same name share one value, so without flattening every copy can end up showing the first copy's answers;
- before you print from a phone or send a form to a print shop;
- before you file it away as a record.
Don't flatten it yet if someone else still has to fill in their part, or if it is going to get a certificate (digital) signature. Flatten first and sign last: any change after a certificate signature shows the document as altered.
Flatten a form in your browser, step by step
- Open PDF Flatten in your browser. There's nothing to install and no sign-up.
- Drag in the filled-in PDF, or several at once.
- Look at the check. It lists what the file holds - form fields, markups and any hidden layers - so you know what is about to be drawn in.
- Flatten and save. The copy is saved beside your download as
name_flattened.pdf; your original is not changed. - Open the copy and click into a box. Nothing should be editable.
The file is read and written inside the browser on your computer. It isn't uploaded, which matters for forms with dates of birth, National Insurance numbers or bank details.
Other ways to flatten, and their catches
| Method | What happens | The catch |
|---|---|---|
| Print to PDF (the Microsoft Print to PDF printer in Windows) | The form is printed into a new PDF, so the boxes go | The whole file is rebuilt as a print: links, bookmarks and page labels are lost, the page can be scaled if fit to page is ticked, and some viewers print fields blank |
| Screenshot or save as a picture | You get an image of the page | Blurry when printed, can't be searched, and much bigger |
| An online flattening website | The file is processed on someone else's server | Your form, with whatever personal details are on it, is uploaded |
| A flattening tool that runs on your computer | Fields and markups drawn into the page, everything else kept | Keep the original if you might need to change an answer |
What flattening doesn't do
- It isn't security. Anyone with a PDF editor can still change text on a page, as they could with any PDF. If you need to prove a document hasn't been changed, use a certificate signature (Fill & Sign PDF Pro does this in the Windows app).
- It doesn't make the file much smaller. For that, see how to compress a PDF without uploading it.
- It can't help with XFA forms. Some older government and bank forms are built with XFA, where the reader app draws the form itself. If a form only shows a "Please wait..." page in a browser, fill it in and print it from the program it asks for.