Signing a PDF needs no subscription and no app. What it does need is a signature image that does not look like it was cut out with scissors.
The built-in route on each platform
| Platform | How | Capture method |
|---|---|---|
| macOS | Preview → Markup → Signature | Trackpad or camera |
| iOS / iPadOS | Markup → + → Signature | Finger or Pencil |
| Windows | Adobe Reader → Fill & Sign | Draw, type or image |
| Android | Adobe Reader or a browser tool | Finger |
| Any browser | Sign PDF — draws or uploads, stays local | Mouse, touch or image |
The macOS camera capture is the best of these and the least known. Sign a piece of white paper, hold it up to the webcam, and Preview lifts the signature and removes the background automatically. The result is far cleaner than anything drawn with a trackpad, and it is stored in iCloud Keychain so it appears on your other Macs.
Making a good signature image
A signature photographed and pasted in without preparation carries a grey rectangle of paper with it, and it shows on any background that is not pure white — which includes most letterheads and every coloured form.
Getting a transparent one is worth the five minutes it takes.
- Sign on unlined white paper with a black pen. A fine liner gives cleaner edges than a ballpoint.
- Photograph it in daylight, straight on, with no shadow across the paper.
- Crop tightly to the signature itself.
- Remove the background so the paper becomes transparent.
- Save as PNG. JPG cannot store transparency, and will reintroduce the white box.
- Keep it large — around 1000 pixels wide. Scaling down is lossless; scaling up is not.
The format point is the one people get wrong repeatedly. Saving a carefully cut-out signature as a JPG silently fills the transparency with white, which is why a signature that looked right in the editor arrives with a box around it.
Signature blocks
A signature block is the structured area around the signature — name, title, date, company — and on a business document it does more work than the mark itself.
For a document you are producing, build it in the source before exporting. Leave a defined space for the signature, then set out the printed name, role and date underneath.
Two conventions worth following. Put the printed name below the signature, because a signature alone is frequently unreadable and the recipient needs to know who signed. And leave the date as something to be filled at signing rather than pre-filling it — a document dated before it was actually signed causes avoidable problems if it is ever examined.
Signing in Word
Word offers two quite different things under similar names, and the distinction matters.
A signature image — Insert → Pictures — is a picture of your signature in the document. It carries no verification of any kind, and anyone with the file can copy it out and reuse it elsewhere.
A digital signature — Insert → Signature Line, then signing it — uses a certificate to bind the signature to the document and to detect later changes. That is a genuinely different mechanism, covered in the next article.
For most business use the image is what is wanted and is entirely normal. Just be aware of what it is: a picture, easily lifted from the file. Do not circulate a Word document containing your signature image any more widely than necessary, and prefer exporting to PDF so the image is at least less convenient to extract.
Filling in the rest of the form
Signing is usually the last step of filling something in, and the fields around it have their own quirks.
If the PDF has real form fields, click and type. If it does not, add text as annotations positioned over the page — visually identical, structurally different, and worth knowing about if the form will be processed automatically.
Text that will not fit a field is a common frustration. Most PDF form fields support auto-sizing: set the font size to 0 or Auto in the field properties and text shrinks to fit as it is typed. On a form you did not build you cannot change that property, so the practical options are to abbreviate, to continue on an attached sheet and write "see attached", or to ask the sender for a version with a larger field. Cramming text into a field that scrolls means the printed copy shows only the part that fits.
Keeping the signature usable
- Store the transparent PNG somewhere you can find it. Recapturing it every time produces inconsistent results.
- Do not email the bare image file. A signature PNG on its own is exactly what someone would want in order to misuse it.
- Flatten the PDF after signing if the signature should not be movable — otherwise it stays an annotation and can be dragged off.
- Check it prints, since annotation layers are occasionally excluded by print settings.
- Use a signing tool that works locally for anything confidential — Sign PDF places and flattens the signature in the browser, so neither the contract nor the signature is uploaded.
The third point catches people out. An unflattened signature is an annotation sitting on top of the page, and the recipient can move or delete it as easily as you placed it.
Frequently asked questions
How do I sign a PDF for free?
Every platform can already do it. macOS uses Preview's Markup signature tool, iOS uses Markup, Windows and Android can use Adobe Reader's Fill & Sign, and browser-based tools work anywhere. None of it requires a subscription.
How do I make a signature image with a transparent background?
Sign unlined white paper with a black fine liner, photograph it straight on in daylight, crop tightly, remove the background, and save as PNG at around 1000 pixels wide. Saving as JPG refills the transparency with white, which is the usual reason a signature arrives with a box around it.
What is the easiest way to capture a signature?
On a Mac, Preview's camera capture — sign white paper, hold it to the webcam, and it lifts the signature and removes the background automatically. The result is much cleaner than drawing with a trackpad, and it syncs to your other Macs.
How do I add a signature block to a PDF?
Build it in the source document before exporting: a defined space for the signature, with the printed name, role and date set out underneath. Leave the date to be filled at signing rather than pre-filling it.
How do I insert a signature in Word?
Insert → Pictures places a signature image, which is simply a picture and carries no verification. Insert → Signature Line creates a field for a certificate-based digital signature, which is a different mechanism entirely. For most business use the image is normal and expected.
How do I shrink text to fit a PDF form field?
Set the field's font size to 0 or Auto and text shrinks as it is typed. On a form you did not create you cannot change that property, so abbreviate, or write "see attached" and continue on a separate sheet. Text crammed into a scrolling field prints only the visible part.
Should I flatten a PDF after signing it?
Yes, if the signature should not be movable. Until it is flattened the signature is an annotation on top of the page, and the recipient can drag or delete it as easily as you placed it.