When you receive a legally binding PDF document (such as a lease agreement or a W-9 tax form) via email, the traditional method of signing it is incredibly inefficient: print the document on paper, sign it with a physical pen, scan the paper back into the computer, and email it back. This destroys image quality and wastes massive amounts of time. You do not need to do this, nor do you need to purchase expensive Adobe software. The native macOS Preview application contains a highly advanced cryptographic signature engine that allows you to legally sign digital documents using your Mac’s trackpad or webcam.
Capturing Your Signature
Before you can sign a document, you must capture a master copy of your physical signature and store it securely inside your Mac’s encrypted keychain.
- Double-click any PDF document to open it in Preview.
- Look at the main toolbar at the top of the window and click the Show Markup Toolbar button (it looks like a small pencil tip).
- Click the Sign icon (it looks like a small cursive signature).
- Click Create Signature.
macOS offers two distinct ways to capture your signature:
Method A: The Trackpad
If you select “Trackpad”, a massive digital canvas will appear on your screen. You can literally trace your physical signature directly onto your Mac’s glass trackpad using your bare finger. The neural engine mathematically translates your finger movements into a smooth, high-resolution vector graphic.
Method B: The Camera
If you prefer the precision of a real pen, select “Camera”. Take a blank piece of stark white paper and sign your name using a thick black pen. Hold the paper directly up to your Mac’s FaceTime webcam. The neural engine will instantly scan the paper, perfectly isolate the black ink, strip away the white background, and digitize the signature flawlessly.
Applying the Signature to a PDF
Once your signature is captured and saved to the system, applying it to a legally binding document takes less than a second.
- Open the PDF contract in Preview.
- Open the Markup Toolbar and click the Sign icon.
- Your digitized signature will appear in a drop-down menu. Click it.
- The signature will instantly drop into the exact center of the PDF page.
- Simply click and drag the signature to the exact signature line on the document. You can drag the blue corner handles to shrink or expand the signature so it perfectly fits the designated space.
When you save the PDF, the Preview application permanently locks the vector graphic into the document’s XML structure, generating a flawless, legally binding digital contract without ever touching a piece of paper.