To flatten a PDF is to merge something that sits on top of the page into the page itself, so it can no longer be changed on its own. What gets merged depends on who asks. Most often it is form fields and comments: a filled form becomes plain page content, and the text stays text. A print shop means transparency: overlapping see-through artwork is cut into opaque pieces. And some tools, Canva among them, mean turning the design into an image, after which there may be no text left at all. On a Mac you can do the first with qpdf or Acrobat Pro, the second with Acrobat Pro, and you should know which one a tool performs before you run it.

What does flattening form fields and comments do?

In a fillable form, each field is an annotation: a box the viewer draws from the field’s value, on top of the page. Comments, stamps and highlights are annotations too. Flattening copies what each one looks like into the page’s own content and removes the annotation, so the value can no longer be changed in the field, and every viewer shows the same thing. Text stays text: you can still select it, search it and copy it.

This is the meaning to expect when an office or a portal asks for a “flattened” form. Fillable versus editable PDFs explains what fields are, and form field defines the terms.

What is transparency flattening?

A print workflow term. Adobe’s help for Acrobat Pro puts it this way: “Flattening divides transparent artwork into vector-based areas and rasterized areas.” Printing and some export formats can require it. Text near transparency can come out as shapes: the option Convert All Text To Outlines, in Adobe’s words, “Converts all type objects (point type, area type, and path type) to outlines and discards all type glyph information on pages containing transparency.” Adobe also warns: “Transparency flattening cannot be undone after the file is saved.”

What does rasterizing a page do?

It replaces the page with a picture of it. Nothing on it is text any more: you cannot select, search or copy the words, and screen readers find nothing. The page behaves like a scan.

Canva uses “flatten” in this sense. Its download dialog has a Flatten PDF setting under Advanced Settings, and its help page explains: “Flattening your PDF converts your design with multiple layers into one.” And further: “This process converts the file into a static image, preventing editing in software like Adobe Acrobat.” Other online tools use the word too, so check what a tool does before you rely on its output: if you can still select a word in the result, it was not rasterized.

Three things flattening can mean Form fields merge into the page as text; transparency is cut into opaque pieces; rasterizing turns the page into pixels. Form fields, comments Merged into the page; the value stays text Transparency Cut into opaque pieces; text may become outlines Rasterizing The page becomes pixels; no text is left to edit
Three things flattening can mean. Only the first keeps the text as text.

How do you flatten a PDF on a Mac?

With qpdf, free and on the command line

qpdf is an open source PDF tool; install it with Homebrew and run:

brew install qpdf
qpdf filled-form.pdf --flatten-annotations=all flattened.pdf

Its manual describes the option: “This option collapses annotations into the pages’ contents with special handling for form fields.” Use print instead of all to keep only what would print, or screen to leave out what is hidden on screen. One caution from the manual: when a form’s appearances are out of date with its values, “If qpdf detects this case, its default behavior is not to flatten those annotations because doing so would cause the value of the form field to be lost.” Save the form again in the app you filled it in, or add --generate-appearances, which the manual says replaces characters outside basic Latin encodings with a question mark.

With Acrobat Pro

Adobe’s guide to flattening goes through the Print Production tools and the Flattener Preview, and says that “After completing these steps, your PDF will be flattened, with all interactive elements like annotations, form fields, and multimedia either removed or integrated into the document’s base layer.” The Flattener Preview is also where the transparency settings live, so check the text option before you apply it.

With Preview

Apple’s guide to filling forms in Preview describes no flatten command. What it does offer is printing to a new PDF: File > Print, then the PDF pop-up menu, then Save as PDF, which writes a new file from the pages as macOS prints them. We have not tested what this route keeps of form fields, so we do not recommend it as a way to flatten. If you try it, check the result the way the next section shows: if a field still takes a click, or pdfinfo still reports a form, it was not flattened.

How can you tell whether a PDF is flattened?

A flattened field no longer takes a click. On the command line, pdfinfo from Poppler reports whether the file still has a form. In our test, a one-field form filled with a name went from this:

Form:            AcroForm

to this, after qpdf --flatten-annotations=all:

Form:            none

and pdftotext still extracted the name as text.

What can PDF Textfix edit after flattening?

Before flattening, PDF Textfix shows form fields but does not fill them, and a field’s text is locked: “This text belongs to a form field or a comment, which viewers draw again from its own value, so it cannot be edited here.” The Issues pane notes once that the form’s fields can’t be filled in PDF Textfix.

After flattening form fields, the value belongs to the page. In our test, qpdf wrote it as a self-contained drawing inside the page (a form XObject, which how a PDF stores text explains), and that drawing carries its own font and sets it before its text. PDF Textfix locks such a drawing when it has no fonts of its own, as the manual’s list of locked lines shows; this one has, so by that rule the value should be editable like any other line. We did not open the flattened test file in PDF Textfix, and other tools may write the value differently: when a drawing takes its font from the page that draws it, the line stays locked and its lock says why. As always, the font decides which characters you can type; in our test file it was Helvetica, named but not embedded.

After transparency flattening with text converted to outlines, or after rasterizing, there is no text to edit: text converted to outlines explains why, and editing text in a scanned PDF covers what OCR can recover.

If you need both, fix the text first and flatten last: flattening is the step that cannot be taken back.

Questions about flattening

Does flattening make a PDF uneditable?

Not by itself. Flattened form values stay text, though whether an editor can change them depends on how the flattening tool drew them and on the editor; check the line’s lock in PDF Textfix. Rasterizing, or converting text to outlines, removes the text itself.

Can you unflatten a PDF?

No. The fields or the transparency are gone from the file. Keep the original if you may need to change the form again.

What does Flatten PDF mean in Canva?

It turns the downloaded design into an image. Canva’s help says that “Flattening a PDF in Canva merges all design elements into a single image, preserving layout and appearance for sharing or printing.” The text then looks the same everywhere but can no longer be edited as text, so keep the Canva design if you may need to change the words.

Is flattening the same as redacting?

No. Flattening a form keeps every word as text, and even a rasterized page can leave text in the file’s metadata or bookmarks. Redacting versus deleting text explains the difference.

How do I flatten a fillable PDF on a Mac for free?

Use qpdf, as shown above: it is free and open source, and pdfinfo confirms the result. We have not tested Preview’s print route on form fields, so we do not recommend it for this.