How to Add a Signature to a PDF for Free (Windows, Mac, iPhone, Android)

To add a signature to a PDF for free: open the file in your device's built-in PDF tool, choose the annotate or fill-and-sign option, and place either a drawn signature or a transparent PNG of your signature onto the signature line. Then save a flattened copy. The whole thing takes under a minute once you have a signature image saved.

What follows is the exact process for each platform, plus the two mistakes that cause almost every "why does my signed PDF look wrong" question.

Method 1: Mac — Preview (built in, free, best on Mac)

Preview has had signature support for years and it is genuinely excellent. It even lets you sign with your trackpad or hold a paper signature up to the camera.

1. 1

   Open the PDF in Preview

   Double-click the file — Preview is the default PDF handler on macOS.

2. 2

   Open the Markup toolbar

   Click the pen-tip icon in the toolbar, or press Shift + Command + A.

3. 3

   Click the signature icon and choose Create Signature

   You get three options: Trackpad (draw with your finger), Camera (hold a signed piece of paper up to the webcam — Preview extracts it and removes the background automatically), or iPhone (sign on your phone screen and it appears on the Mac).

4. 4

   Click your saved signature to place it

   It drops onto the page. Drag it to the signature line and resize using a corner handle so the proportions stay correct.

5. 5

   Save a flattened copy

   File → Export as PDF. This bakes the signature into the page instead of leaving it as an annotation.

Method 2: Windows — Microsoft Edge (built in, free)

Windows has no first-party PDF editor, but Edge is the default PDF viewer and it can draw and save. It is limited — freehand drawing only, no reusable saved signature — so pair it with an image method if you sign often.

1. 1

   Right-click the PDF → Open with → Microsoft Edge

   The file opens in the browser's PDF viewer.

2. 2

   Click Draw in the top toolbar

   Pick black or blue ink and set the thickness to around 3 for a natural pen weight.

3. 3

   Draw your signature on the signature line

   A stylus or touchscreen beats a mouse here by a wide margin.

4. 4

   Save

   Ctrl + S writes the annotation into the file.

For a reusable signature image on Windows, use a free desktop reader that supports stamps — Adobe Acrobat Reader (the free tier includes Fill & Sign), Foxit Reader, or PDF-XChange Editor all let you save a signature once and reapply it. In Acrobat Reader: Sign → Add Signature → Image, then upload your transparent PNG.

Method 3: iPhone and iPad — Markup (built in, free)

This is the best experience of the lot, because you are signing with your finger or an Apple Pencil on glass, which produces a natural line.

1. 1

   Open the PDF

   From Files, Mail, or Messages — tap the attachment to preview it.

2. 2

   Tap the Markup icon

   The pen-tip circle, usually top right.

3. 3

   Tap + then Signature

   Add a new signature by drawing it, or reuse one you saved earlier.

4. 4

   Position and size it

   Drag it to the line and pinch to resize.

5. 5

   Tap Done, then share or save

   The markup is written into the PDF.

Method 4: Android

Android has no universal built-in PDF annotator, so behaviour varies by manufacturer. Two reliable routes:

• Adobe Acrobat Reader (free) — open the PDF, tap the pencil icon, choose Fill & Sign, then Create Signature. Draw it or import a PNG. Signatures persist for reuse.
• Google Drive preview — open the PDF in Drive, tap the annotate pencil, and draw. Fine for a quick signature, but there is no saved-signature feature.

Samsung devices with an S Pen handle this particularly well through Samsung Notes, which produces a smooth pressure-sensitive line.

Method 5: Browser — works on any device

If you are on a locked-down work machine, a Chromebook, or a device you do not want to install anything on, a browser tool is the answer.

1. 1

   Create your signature image first

   Use a free signature generator to produce a transparent PNG. This runs in your browser, so the signature never leaves your device.

2. 2

   Open a browser-based PDF editor

   Any tool that lets you place an image onto a PDF page will do.

3. 3

   Place the PNG on the signature line

   Because it is transparent, only the ink shows — nothing underneath gets covered.

4. 4

   Download the signed PDF

   Check it opens correctly and the signature sits where you intended before sending.

The two mistakes that ruin signed PDFs

1. A white box around your signature

This means your signature image is a JPG, or a PNG whose background was never made transparent. JPG has no alpha channel, so it always carries a rectangle of white — which sits on top of the signature line, the date field, and anything else beneath it.

The fix is to start from a transparent PNG. Our guide on making a transparent signature PNG covers how to strip a background from a scan in free tools.

2. Leaving the signature as a movable annotation

Some tools save your signature as an annotation layer rather than as page content. The recipient can then click it, drag it, or delete it — which is bad for you and confusing for them.

Flattening merges the annotation into the page. Depending on the tool this is called Export as PDF (Preview), Print to PDF, Flatten, or Save a Flattened Copy. When in doubt, printing to PDF always flattens.

Signing a PDF vs sending one for signature

Everything above covers signing a document that arrived in your inbox. The reverse job — sending a contract to a client and getting it back signed — is a different problem, and doing it by emailing a PDF back and forth has real costs.

For a $500 job, emailing a PDF is fine. For a $50,000 build with three parties and a payment schedule, the audit trail is the point. We cover the difference in how to send a contract for signature.