How to flatten a signed PDF on iPhone

You signed a PDF on your iPhone, sent it back, and something went wrong. The sender says the signature didn’t print. Or they opened it and the signature slid halfway down the page. Or they mention, a little too casually, that they could just delete it.

None of that is a bug in your signature. It’s a bug in how it was attached. And the fix has a name: flattening.

What “flattening” actually means

A PDF page has content — the text and images the document was made of. On top of that, a PDF can carry annotations: comments, highlights, stamps, and the signature images that iOS Markup adds. Annotations sit in a separate layer. They’re deliberately editable, because that’s what annotations are for.

That layer is why signed PDFs misbehave:

It can move or be deleted. Anyone who opens the file in a viewer that supports Markup can drag your signature or remove it entirely.
It can fail to print. Some printers and print drivers ignore annotations, so the page comes out with a blank signature line. This is the single most common complaint, and it’s why people go looking for this page.
It can render differently. A viewer that doesn’t support the annotation type may show nothing at all.

Flattening merges that layer down into the page itself. Afterwards there is no separate signature object — there is just a page that has your signature printed on it, the same way the document’s own text is printed on it. It prints everywhere, renders everywhere, and can’t be dragged off.

The free route: Print to PDF (no app needed)

iOS has a flattener built into the print system, and it costs nothing.

Open the signed PDF — in Files, or from the Mail attachment.
Tap the Share button, then scroll down and tap Print.
Wait for the preview thumbnail to render. You don’t need a printer connected.
On the print preview screen, tap the Share button in the corner (on older iOS versions, pinch outward on the thumbnail first, then Share).
Choose Save to Files — or share it straight into your reply.

What you get back is a brand-new PDF, re-rendered from what the print system saw. The signature is now part of the page.

The honest tradeoffs, because there are real ones:

It’s one-way. The new file has no editable annotation layer, which is the point — but it means you can’t nudge the signature afterwards, and you can’t remove a signature from a PDF on iPhone once it’s been flattened either. Keep the original until you’ve checked the result.
You may lose extras. Fillable form fields, clickable links, and bookmarks usually don’t survive the round trip. If the recipient still needs to fill fields in the same file, don’t flatten it yet.
Quality can drop a little. The output is re-rendered, so on a scan-heavy document the file size and sharpness may shift.

For a one-off signed form heading straight to someone’s inbox, that’s a fine trade. For a form that still has to be filled in, it isn’t.

The same Print → Share → Save to Files route does double duty, incidentally: it’s also how you sign a PDF on iPhone that is password protected once you’ve opened it with the password, since the copy it produces comes out without the password attached.

On a Mac, if you have one nearby

Same idea, cleaner tools: open the PDF in Preview, then File → Print → PDF → Save as PDF. Preview’s File → Export also drops annotations into the page on most documents. If you’re already at a desk, this is the least fiddly version.

How to check whether a PDF is actually flattened

Don’t take it on trust — this takes ten seconds.

Open the file in Files, tap the Markup (pencil) icon, and try to tap your signature. If it selects, shows handles, or drags — it’s still an annotation and it’s still fragile. If nothing happens and it behaves like the printed text around it, it’s flattened.

The second check: print it, or send it to a Print-to-PDF and look at the output. If the signature survives that, it will survive the recipient’s printer.

Signing so you never have to flatten afterwards

Flattening is a repair step. If you sign documents regularly, the better move is to not create the problem.

That’s what a signing app does differently. In Signed, you import the PDF, drop your saved signature, date and initials where they belong, and tap Finish — and the file it hands you is already flattened. There’s no annotation layer to lose, no print-to-PDF detour, and no version of the file where your signature is a draggable sticker.

Two things worth knowing while you’re here:

Your signature is saved once and reused, so the second document takes seconds rather than a fresh finger-drawing on glass.
The whole thing runs on the device. Signed is local-first — the PDF isn’t uploaded anywhere to be processed, which is a meaningful difference from the flatten-my-PDF websites that ask you to hand over the document first.

What flattening does not do

This part matters, because plenty of pages on this topic blur it.

Flattening is a rendering fix, not a security feature. It stops casual edits — the recipient can’t grab your signature and drag it. It does not make the document tamper-proof: anyone with real PDF editing software can still alter a flattened page, and a flattened signature is not a cryptographic signature or a certificate.

It also has nothing to do with whether the document is accepted. Whether a signature satisfies the requirement for a particular document depends on the document and the jurisdiction — some need a witness or a notary regardless of how you produced the file. Flattening changes how the file behaves in a PDF viewer. That’s all it changes, and that’s genuinely useful, but it’s worth being clear about the boundary. See are electronic signatures accepted? for the honest version of that question.

The short answer

Signature didn’t print, or the recipient can move it? It’s an unflattened Markup annotation.
Free fix, right now: Share → Print → Share from the print preview → Save to Files.
Keep the original — flattening is one-way, and it can drop form fields and links.
Signing more than occasionally? Use a tool that exports flattened in the first place, and skip the repair step entirely.