How-to guide
How to add a signature to a PDF
Every device you own can already place a signature on a PDF — Adobe Reader and Microsoft Edge on Windows, Preview on Mac, and the built-in markup tools on iPhone and Android. The one thing they all need is a clean signature, and that's the part you can prepare here in seconds.
Before you start: you'll need your signature as an image. The signature for PDF tool exports a transparent PNG sized for contract signature lines — free, no account, and nothing you type leaves your browser.
Why PDF is where most signing actually happens
Whatever format a document starts in, it usually becomes a PDF the moment signatures are involved — because PDF freezes layout, prints identically everywhere, and makes post-signature editing awkward enough to discourage casual tampering. That's why every serious operating system has grown built-in PDF markup: Adobe Acrobat Reader on Windows and Mac, Preview on macOS, Edge on Windows, and native markup on both iPhone and Android.
All of these tools share one gap: they can draw a signature with your mouse or finger, but drawn-on-a-trackpad rarely looks like your real signature. The fix is to prepare the signature once as a transparent PNG and let the PDF tool place it. Acrobat Reader even remembers the image permanently — set it up one time and every future document is a two-click sign.
A note on terminology before the steps: placing a signature image on a PDF creates an electronic signature, which is what nearly all everyday documents need. Some regulated workflows require a certificate-based digital signature instead — if a sender asks for that specifically, they'll typically route you through a platform like DocuSign, and none of these steps are needed. Our legality guide explains the difference in depth.
Step by step
Create your signature
Type or draw your signature and download the transparent PNG. Transparency is what makes it sit on the PDF's signature line without a white box.
Adobe Acrobat Reader (Windows/Mac)
Open the PDF, choose Fill & Sign in the tools panel, click Add signature, and pick Image to load your PNG. Acrobat remembers it for every future document — click the signature line to place it, drag to resize.
Microsoft Edge (Windows, no install)
Edge opens PDFs natively. Use the Draw pen to sign directly, or for a cleaner result print-to-PDF after inserting your PNG in Word. For frequent signing, Acrobat Reader's image method is more precise.
Preview (Mac)
Open the PDF in Preview, click the markup toolbar, then Sign. You can create a signature with the trackpad or camera — or drag your PNG straight into the page and resize it over the line.
iPhone and iPad
Open the PDF (Files app or Mail attachment), tap the markup pen icon, then + → Signature. Sign with your finger, or paste your prepared signature image into the page.
Android
Open the PDF in Google Drive, tap the pen icon to annotate, and sign with your finger — or use Adobe Reader's free Android app with the same Fill & Sign flow as desktop.
Troubleshooting
Fill & Sign won't let me add an image
You're in the "Request signatures" flow instead of "Fill and sign yourself". Choose the self-sign option; the Image choice appears when you click Add signature.
My signature has a white box on the PDF
The image isn't transparent. Re-export as transparent PNG — the signature for PDF tool does this by default — because a white rectangle over a form line is the clearest tell of an amateur signing job.
The PDF won't accept any annotations
It carries editing restrictions. Print it to a new PDF (Ctrl+P → "Save as PDF" / "Microsoft Print to PDF") and sign the copy — the restriction doesn't survive printing.
Signature placed fine but prints tiny/huge
PDF viewers place images at their pixel size relative to page DPI. Resize with the corner handles until it matches the line visually before saving; what you see in the viewer is what prints.
Best practices
- Set your signature up in Acrobat Reader once with the Image option — it syncs into the free mobile app too, giving you two-click signing everywhere.
- Save the signed file under a new name (contract-signed.pdf) so the unsigned original stays available.
- Flatten when it matters: printing the signed PDF to PDF again merges the signature into the page, preventing anyone from lifting the image out.
- On a phone, sign with your finger only for low-stakes documents; for contracts, paste your prepared PNG for a consistent mark.
Common questions
How do I sign a PDF without Adobe?
Microsoft Edge, macOS Preview, Google Drive, and most browsers can annotate PDFs for free. The transparent-PNG-plus-Fill&Sign route just gives the most polished result.
Is a signature placed on a PDF legally binding?
Usually yes, for the same reason typed signatures are — intent to sign is what courts look at. Regulated documents sometimes require certificate-based digital signatures; our legality guide covers the difference.
The PDF is locked and won't let me sign — what now?
If the PDF has editing restrictions, print it to a new PDF first (Ctrl+P → Save as PDF), then sign the copy. If it's password-protected, you'll need the password from the sender.
How do I sign a PDF on a Chromebook?
Open the PDF in Chrome's built-in viewer and use the pen annotation, or open it with the Gallery app which includes markup. For image placement, the free Acrobat web app (acrobat.adobe.com) offers Fill & Sign in the browser.
Can I remove or change a signature after saving?
If you saved without flattening, the image can often be selected and deleted in an editor. Once printed-to-PDF or flattened, the signature is part of the page image — which is exactly why flattening is recommended before sending.
What size should a PDF signature be?
Match the signature line: typically 4–6 cm wide on an A4/letter contract. The signature-for-pdf tool exports at proportions sized for standard contract lines, so dragging one corner usually gets it right.