How to sign a PDF on iPhone and keep the form fields editable

You filled in your part of a PDF form on your iPhone, signed it, and sent it on. Then the next person replies: they can’t type in their section. The boxes that used to open a keyboard are now just pictures of boxes. Or it happens to you: you sign first, go back to fix a typo in the address field, and the field is dead.

Signing didn’t have to do that. Whether the fields survive depends entirely on how the app you signed with saves the file, and you can choose. This page is how to choose, and how to check the result before anyone else finds out the hard way.

Why signing can kill the fields

A fillable PDF has two kinds of things on each page. There’s the page content (the printed text and lines), and there are interactive form fields sitting on top: text boxes, checkboxes, dropdowns. The fields are what make the keyboard appear when you tap.

When you add a signature, an app can save the result in one of two ways:

As an annotation. The signature is added as one more object on top of the page. Everything else in the file, including the form fields, is left alone. The form stays a form.
Flattened. The app redraws every page into a brand-new PDF with the signature baked in. The new pages show what the fields looked like, typed values included, but the fields themselves are gone. Nothing is tappable any more.

Neither is wrong. Flattening is the right result for a finished document, because a flattened signature prints everywhere and can’t be dragged off the page. It’s the wrong result for a form somebody still has to fill in. The trouble is that most apps pick one for you and don’t say which.

First decide: should this form stay open or close?

Ask one question before you sign: is anyone going to type in this file after me?

Yes (a co-applicant, a manager, HR, the other party, or you later): the form must stay open. Sign in a way that keeps the fields, as described below.
No, I’m the last one: you probably want it closed. A finished form whose fields are still live can be edited by anyone who opens it. Flatten it and send. How to flatten a signed PDF on iPhone covers that side in full.

If you’re not sure who signs when, how two people can sign the same PDF on iPhone walks through the order. The short version: the person who flattens must go last.

How to sign and keep the fields: the free route

Apple’s built-in Markup adds a signature as an annotation, which is the kind that leaves the rest of the file alone. So the free route is also the right one here.

Save a spare copy first. In Files, long-press the PDF and tap Duplicate. Keep the untouched original until everyone has finished. This one step makes every mistake below recoverable.
Fill in your fields. Open the PDF in Files and tap each field to type. If nothing is tappable, the PDF never had fields to begin with, which is a different problem: see why you can’t type in a PDF on your iPhone.
Add your signature with Markup. Tap the Markup (pen tip) icon, tap +, then Signature. Pick your saved signature or draw a new one, drag it onto the line and size it. If the form has no signature box, that’s fine; you can sign a PDF that has no signature field by placing it anywhere.
Tap Done to save.
Run the check below before you send it. Don’t skip this. iOS versions and individual PDFs differ, and the check is the only thing that actually tells you what your file did.

When you send it on, share the PDF file itself from the share sheet. Do not use Print, and do not use any “save as PDF” or “export” detour: on iPhone those re-render the document, which flattens it and removes the fields.

The 20-second check

Close the file completely, then reopen it from Files, so you’re looking at what was saved and not what’s still in memory.

Tap a field you left empty. If the keyboard opens, the fields survived.
Tap a field you filled in and change a letter. If you can edit it, the form is still fully open.
If nothing responds, the file was flattened. Go back to your duplicate and sign again by a different route. A flattened file can’t be un-flattened.

The check works on a file from any app, and it’s worth doing even when you think you know what the app does.

What the common apps do

How you signed	What usually happens to the fields
iOS Markup signature, saved with Done	Kept. The signature is an annotation on top of the form. Confirm with the check.
Share → Print → save from the print preview	Removed. This is a re-render, and it’s the standard way to flatten on purpose.
Adobe Acrobat Reader’s Fill & Sign	Often locked once a signature is added and the file is saved. Adobe treats a signed form as finished, and its own forum has long threads from people surprised by this. Fill everything in before you sign, and keep an unsigned copy.
A signing app that exports a “signed copy” (Signed included)	Removed. The export is a flattened PDF by design.
A certificate-based digital signature	Depends on the form’s author. The form can be set to lock some or all fields the moment it’s signed, and that is deliberate.

That last row is worth a second look. If a form came from a bank, a law firm or a government office and carries a cryptographic signature field, the locking is a feature the sender configured, and editing the file after signing can break the signature. An iPhone generally can’t apply that kind of signature anyway. Ask the sender how they want it handled instead of working around it.

If you’ve already signed and the fields are gone

You kept the original: open it, fill in the fields again, and sign with Markup this time. Annoying, but five minutes.
You didn’t keep it: ask whoever sent the form for a fresh copy. That’s a normal request and usually the fastest fix.
Neither is possible: the next person can still complete a flattened form by placing text on top of it, the same way you’d fill in a scan. How to fill out and sign a form on iPhone covers that. It works, but they’re typing over a picture of a form, not into the form.

Where Signed fits, and where it doesn’t

Signed is a PDF signing app for iPhone, and for this particular job it is the wrong tool. That’s worth saying plainly on a page with its name at the top.

When you tap Finish in Signed, the app redraws every page of the document into a new PDF with your signature, date, initials and any text you placed baked into it. Whatever you had typed into the form’s fields is still visible, but the exported file has no fillable fields at all. There’s no setting to change this. Signed also doesn’t type into a PDF’s interactive fields in the first place; it places its own text on top of the page wherever you tap.

So:

Someone still needs to fill in the form after you: don’t use Signed for this step. Use Markup as above.
You’re the last signer and the form is complete: this is what Signed is for. The file it hands back is closed. The signature can’t be dragged or deleted in a PDF viewer, it prints on every printer, and nobody can casually retype the fields. Your signature is saved once and reused, and the document stays on your iPhone the whole time.

One limit on that, so it isn’t oversold: flattening stops casual edits, not determined ones. Anyone with real PDF editing software can still alter a flattened page. It’s a tidy, finished file, not a tamper-proof one.

The short answer

Signing doesn’t have to lock a form. Flattening does, and many apps flatten when they save a signed copy.
To keep fields editable on iPhone: duplicate the file, fill your fields, sign with Markup, tap Done, and share the file itself. Never go through Print.
Reopen it and tap an empty field before sending. That check beats any rule of thumb.
If you’re the last to sign, closing the form is the goal. Flatten it then, and not before.

Signed is a signing tool, not legal advice. Whether a form has to stay editable, and who is allowed to change it after it’s signed, is up to whoever issued it. If it matters, ask them.