everyday mac tools

Sign a PDF on a Mac using Preview

· 5 min read

Open the PDF in Preview, show the Markup toolbar, click the Signature button and create a signature with the trackpad, the camera or your iPhone. Drag it onto the signature line, resize it, add the date with the Text tool, and save. That is the whole procedure for most documents.

The rest of this post covers the details that catch people: making the signature part of the page so it cannot be moved, what this kind of signature actually is, and what to do when someone asks for a “digital signature” and means something different.

Create the signature once

Preview keeps signatures after you create them, so this is a one-time job.

  1. Open any PDF in Preview and choose View, Show Markup Toolbar (or click the pen-tip icon in the toolbar).
  2. Click the Signature button. It looks like a scribble on a line. If you have no signatures yet, the panel opens straight to Create Signature. Preview also lists the Signature tool under Tools, Annotate.
  3. Pick a method: - Trackpad. Click Click Here to Begin, sign with your finger on the trackpad, and press any key when you finish. Signing with a finger takes a couple of tries; slow strokes come out better than fast ones. - Camera. Sign your name in black ink on white paper, hold it up to the Mac’s camera, and line it up with the blue line on screen. Preview traces the ink and drops the paper background. - iPhone or iPad. If the device is nearby and signed in to the same Apple Account, this tab lets you sign on its screen with a finger or an Apple Pencil, which produces the most natural result of the three.
  4. Click Done. The signature is saved and appears in the Signature menu from now on.

You can keep more than one, for example a full signature and initials. Hover over one in the list and click the X to remove it.

Place it on the page

  1. Click the Signature button and choose the signature you want. It appears in the middle of the page.
  2. Drag it to the signature line. Drag a corner handle to resize it; the proportions stay fixed.
  3. For the date or a printed name, choose the Text tool from the same toolbar, type, and drag the box into place. Font and size are adjustable from the toolbar.
  4. Save (Command-S).

If the document is also a form with fields to fill in, do the fields first and the signature last. Fill in a PDF form on a Mac and flatten it so it stays filled covers the form side.

Make it stay put

A signature added in Preview is an annotation: an object sitting on top of the page, like a highlight or a note. Depending on the reader that opens it next, an annotation can be selected, moved, resized or deleted. For a document that is about to become a record, that is not what you want.

The fix is the same one that flattens a form. Print the document to a new PDF, and the annotation is drawn into the page itself.

  1. Choose File, Print.
  2. Open the PDF menu at the bottom-left of the print dialog and choose Save as PDF.
  3. Save under a new name and send that file.

Open the result and try to click the signature. Nothing selects, because it is now pixels and lines on the page rather than a separate object. Links in the document stop being clickable at the same time, and any bookmarks are dropped; for a signed contract, that rarely matters.

What kind of signature this is

This is the part worth reading before you send anything that matters.

A Preview signature is a picture of your handwriting placed on a page. It shows that someone put your signature there. It does not prove who, or when, or that the document has not changed since. In practical terms it is the same as printing the document, signing it with a pen and scanning it back in, minus the printer.

A digital signature in the technical sense is different: it is a cryptographic seal tied to a certificate, and a reader that supports it can verify that the certificate belongs to a named person and that not one byte of the document has changed since it was applied. Preview does not create these, and it does not verify them either; a PDF carrying one opens in Preview like any other PDF, with no indication of whether the seal is valid.

If a bank, a court, a government portal or a counterparty’s legal team asks for a digital or certified signature, they mean the cryptographic kind, and they will usually tell you which service or format they accept. A signature drawn in Preview will be rejected. For everything else, including most contracts between people who already trust each other, the picture is what has been used for decades and it is fine.

Signing on an iPhone instead

If the PDF is in iCloud Drive or arrives by email, you can sign it on the phone without the Mac. Open it in the Files app or from Mail, tap the Markup button (the pen tip), tap the plus button and choose Signature. The signatures you created in Preview may already be there if iCloud Keychain is on; if not, draw one on the screen. Save, and the file syncs back.

The result is the same kind of annotation as on the Mac, with the same caveat about flattening before sending.

Signing many documents

For a document a week, Preview is all the tool you need. If your work involves signing, dating and stamping a stack of PDFs, the print-to-flatten step and the “is the original still untouched” worry both start to cost time.

Basalt includes a Sign tool alongside its Forms and Watermark tools in one window, and like every Basalt tool it writes a new file and leaves the original alone, so the unsigned version is always there to go back to. It runs entirely on the Mac with no account and no upload. It does not create certificate-based digital signatures either; nothing in this post does, and any app that claims a drawn signature is one is overselling.

Questions

Is a signature made in Preview legally valid? In many places an electronic signature is valid when both sides intend it to be, and an image of a handwritten signature is one common form. Whether it is accepted for a particular document depends on the law where you are and on who is receiving it, not on the Mac. If it matters, ask the recipient what they require before you sign.

Can I sign a scanned PDF? Yes. The signature is placed on top of the page, and it does not matter whether the page underneath is text or a scanned image. Flatten it afterwards in the same way.

Where does Preview keep my signatures? In your keychain, so they are protected by your login and not stored as loose image files. Deleting one from the Signature menu removes it. If you share a Mac account with someone, they can see and use your saved signatures, which is one more reason not to share an account.

Can someone lift my signature out of a PDF and reuse it? If it is left as an annotation, easily. If it is flattened into the page, it is harder but still possible by cropping the image, in the same way a signature on paper can be photocopied. Do not send an unflattened signed PDF to someone you do not trust, and do not treat any drawn signature as a secret.