How to Add a Signature to a PDF on Phone or Desktop

Signing a PDF has become one of those tasks that looks like it needs software and does not. Every current phone and both desktop operating systems can place a signature on a page, and the built-in tools produce a better result than most free apps because they capture the signature with a transparent background.

The part people get wrong is the image. A photograph of a signature on paper is an opaque rectangle, and dropping that onto a document gives you handwriting inside a visible grey box. The methods below avoid that.

Pick the route for your situation

That last row matters. If the sender used a signing service, use the link they sent rather than signing a downloaded copy — their system records who signed and when, and a separately signed copy emailed back usually has to be redone.

iPhone and iPad

The fastest route on any platform, because the signature capture and the PDF editor are the same tool.

1. Open the PDF — from Files, Mail or the share sheet.
2. Tap the markup icon (a pen tip).
3. Tap + at the bottom right → Signature.
4. Sign with your finger, or an Apple Pencil if you have one. Tap Done.
5. Drag the signature where it belongs and resize it with the corner handles.
6. Tap Done and save, or share it straight from the markup view.

The signature is stored for reuse, so the next document takes five seconds. To replace a badly drawn one, open the signature list and swipe to delete it.

A finger signature looks like a finger signature. If the document is important, sign on paper, photograph it, and use the camera capture option in the Mac method below — or sign slowly, zoomed in, which helps more than you would expect.

macOS Preview

Preview has the best capture options of any of these, including one that reads a signature from paper.

1. Open the PDF in Preview.
2. Click the markup icon (a pen tip) in the toolbar.
3. Click the Signature icon → Create Signature.
4. Choose how to capture it:
   • Trackpad: sign with your finger on the trackpad. Awkward but quick.
   • Camera: sign on white paper, hold it up to the camera, and Preview extracts the strokes with a transparent background. This gives the best result by a wide margin.
   • iPhone: sign on a connected iPhone or iPad screen.
5. Click the saved signature to place it, then drag and resize.
6. File → Save, or File → Export as PDF to keep the original untouched.

The camera option is the one to use. Sign on unlined white paper with a dark pen, fill a reasonable portion of the sheet, and hold it steady against the blue guideline. Preview separates the ink from the paper, so you get real handwriting with no background.

Windows

Windows has no system-wide signature store, so there are two approaches.

Edge’s PDF tools

Open the PDF in Edge and look for the Draw tool in the toolbar. Choose a dark colour and a thin stroke, then sign with a mouse, trackpad or touchscreen. Save with Ctrl+S.

Mouse signatures look like mouse signatures. On a touchscreen laptop this works acceptably; with a mouse it rarely does.

A transparent PNG, prepared once

More setup, far better results, and reusable forever.

1. Sign on plain white paper with a dark pen, filling a good portion of the page.
2. Photograph or scan it. A scan at 300 DPI is better than a photo; a photo in even light is fine.
3. Remove the background. Windows Photos and the Paint background-removal tool both manage this on a high-contrast image. Save as PNG — JPG cannot store transparency, which is the whole point.
4. Insert it into the PDF. Word handles this if you are generating the document; for an existing PDF, a viewer with an image stamp tool is needed.

Crop tightly around the ink before saving, and keep the file at a reasonable size. A 4000-pixel signature image dropped onto every page of a contract adds real weight to the file, which is one of the quieter contributors described in why PDFs become large.

If you end up with a signature saved as a JPG and need it transparent, it has to be re-made rather than converted — our PNG to JPG converter goes the other way, and no tool can invent transparency that a JPG never stored. Resizing a signature for an online form covers getting the dimensions right when a form demands them.

Android

Android has no consistent built-in answer, because PDF handling differs by manufacturer. Samsung devices with an S Pen have markup tools in their own viewer. Google Drive’s PDF preview offers annotation on some versions.

The reliable fallback is Google Docs: open the PDF in Drive, insert a signature image, and export. Clumsy, but it needs nothing installed.

Drawn signatures versus digital signatures

Worth being clear about, because the terms are used interchangeably and mean different things.

A drawn signature is an image placed on a page. It shows intent, which is what most agreements need. It proves nothing about who placed it or whether the document changed afterwards.

A digital signature is cryptographic. It binds a certificate to the exact bytes of the document, so any later alteration invalidates it, and the viewer shows who signed and whether the file has been modified. This is what regulated contexts require.

If a form says “digitally signed” and refuses your drawn signature, that distinction is why, and no drawing tool will satisfy it.

What to expect

A camera-captured signature in Preview, or a finger signature on an iPhone, takes under a minute and looks like a signature rather than a drawing. Both store it for reuse.

The honest limit is that none of this makes a document more legally robust than the agreement behind it. If the receiving party has specific requirements — witnessed, digitally signed with a recognised certificate, or wet-ink original — a drawn image will not satisfy them, and finding that out before you send is cheaper than finding out afterwards.