Every platform can sign a PDF without installing anything. The routes differ enough that people assume theirs cannot.
What each platform gives you
| Device | Built in? | Route |
|---|---|---|
| iPhone / iPad | Yes | Markup — open, tap the pen, then the signature tool |
| Mac | Yes | Preview — Markup toolbar, then Sign |
| Windows | No | Edge can draw; a proper signature needs a tool |
| Android | Varies | Samsung and some others include markup; many do not |
| Chromebook | Partly | The Gallery app annotates; no signature store |
| Any browser | Yes | Works identically everywhere |
Apple's advantage here is real: signing on an iPad with a finger or a pencil produces the most natural-looking signature of any method, because it captures actual handwriting rather than a mouse gesture.
Signing a document that arrived by email
This is the common case, and the mistake is doing it in the mail client.
Most mail clients show a preview rather than the file. Annotating a preview marks a temporary copy, and the reply then attaches the original unsigned document — a mistake nobody notices until the other party asks again.
- Download the attachment properly, to Files or Downloads. Do not work in the preview.
- Sign the downloaded file.
- Confirm the file size changed, which tells you the signature was written into it.
- Attach the signed file to the reply explicitly, rather than using Reply on a thread that may re-attach the original.
On iOS the trap is sharper: tapping an attachment opens Quick Look, and Markup there sometimes edits a copy that Mail discards. Save to Files first.
Google Drive
Drive previews PDFs but does not sign them. Opening one in Google Docs converts it — the layout usually breaks and the result is not the document you were sent.
The workable route is to download, sign locally, and upload the signed file as a new version rather than a new file, so the link you already shared keeps working.
If the document is an eSignature request from a service, use their link rather than downloading. Those flows record an audit trail — IP, timestamp, email verification — which a drawn signature on a downloaded copy does not have.
Making the signature look real
A signature drawn with a mouse looks exactly like a signature drawn with a mouse, and on a contract going to a client that matters.
- Best: sign paper and photograph it. Black ink on white, daylight, then remove the background with the Background Remover so it drops onto the page cleanly rather than as a grey rectangle.
- Good: draw on a touchscreen. A finger on a phone beats any mouse. A stylus beats a finger.
- Acceptable: draw large and scale down. Detail survives shrinking; it does not survive enlargement.
- Keep it PNG. JPEG has no transparency, so the signature arrives inside a white box sitting over the signature line.
Reuse one good signature image rather than redrawing each time. It looks consistent, which is itself a signal of authenticity — a signature that differs wildly between documents invites the question.
On a shared or work computer
Two things worth thinking about before signing on a machine that is not yours.
A signature image is a reusable credential. Unlike a password it cannot be changed, so leaving one in a Downloads folder or saved in an application's signature store on a shared machine is a genuine exposure.
And an upload-based signing tool has your signature and the document. For an NDA or an employment contract that is worth avoiding on principle.
A browser-based signer keeps both on the machine, which narrows the problem to that machine. The Sign PDF tool does the work locally — you can confirm it by opening the Network tab before signing. Then delete the downloaded files when you are done.
Frequently asked questions
Can I sign a PDF on an iPhone without an app?
Yes. Open it in Files, tap the Markup pen, then the signature tool. iOS stores a signature for reuse. Save the file to Files first rather than signing inside a mail preview, which sometimes edits a copy that gets discarded.
How do I sign a PDF on Windows?
Windows has nothing built in. Edge lets you draw on a PDF but has no signature store, so a browser-based signing tool or a PDF reader is the practical route. A browser tool avoids installing anything.
Why did my signature not appear in the reply?
You almost certainly signed a preview rather than the file. Most mail clients show a temporary copy, so the reply re-attaches the original unsigned document. Download the attachment properly, sign that, and attach it explicitly.
Can I sign a PDF in Google Drive?
Not directly — Drive previews but does not sign, and opening in Google Docs converts the file and usually breaks the layout. Download, sign locally, then upload as a new version so any link you shared keeps working.
What is the best way to make a signature look natural?
Sign paper in black ink, photograph it in daylight, and remove the background so only the ink lands on the page. That captures real pressure variation. Failing that, draw on a touchscreen with a stylus — a mouse always looks like a mouse.
Is it safe to sign on a shared computer?
Be careful. A signature image is a credential you cannot revoke, so leaving one in Downloads or in an app's signature store is a real exposure. Use a tool that works locally, and delete the files afterwards.