How to insert a signature into a PDF (without Adobe)

Most people associate PDF signatures with Adobe Acrobat, which costs around £15–20 per month for the full version. That's more than most individuals need to spend to put their name on a contract. Several free and low-cost alternatives do the job just as well for most signing scenarios.

Method 1: browser-based e-signature tool (strongest legal standing)

Upload the PDF to an e-signature platform — InkRobin, Dropbox Sign, DocuSign — drag a signature field to the right position in the document, and sign. The entire process happens in your browser with no software to install. You can also send the document to someone else for their signature and receive the signed copy by email when they're done.

What this produces: a PDF with your signature visually embedded, plus a Certificate of Completion (or equivalent) that records the signing event — your email address, the time and date, your IP address, and a hash of the document. This is what makes the signature legally defensible if it's ever challenged.

• Upload your PDF to InkRobin
• Click the signature field tool and drag it to where the signature should appear
• Choose to sign yourself (type, draw, or upload your signature) or send a signing link to another party
• Once signed, download the completed PDF

Method 2: Mac Preview (quick and free)

Open the PDF in Preview, click the Markup toolbar icon, then the signature button. You can draw a signature using your trackpad, sign on paper and hold it up to the camera, or sign using your iPhone if it's nearby. Once saved to Preview, your signature appears as an overlay on the PDF.

What this produces: a PDF with a signature image on it. There's no timestamp, no IP record, no document hash. For signing your own personal documents (tax forms, internal paperwork), this is perfectly adequate. For a contract between two parties where a dispute could later arise, it's not strong enough.

Method 3: mobile phone (fastest for informal documents)

On iPhone, open the PDF in Files, tap the share button, and open it in Markup. The signature tool is in the plus menu. On Android, Adobe Acrobat Reader (free version) lets you fill and sign PDFs. You draw your signature with your finger and tap to place it. Again — quick, free, and produces an annotated PDF rather than a signed document with an audit trail.

When does the method actually matter?

It matters most when you need to prove that a specific person signed a specific document at a specific time, and that the document hasn't changed since. Courts look for attribution (who), timing (when), and integrity (unchanged document). A signature image on a PDF proves none of these. An e-signature with an audit trail proves all three.

For informal purposes — signing a form for yourself, acknowledging a policy document, internal workflows — the simpler methods work fine. For client contracts, lease agreements, service agreements, and NDAs, use an e-signature platform that produces an audit trail.

Frequently asked questions

• Can I insert a signature into a PDF for free? Yes — InkRobin's free plan covers five documents per month. Mac Preview is free. Adobe Acrobat Reader (basic version) is free.
• Is a PDF signed in Preview legally valid? It can be, but attribution is difficult to prove without an audit trail. For anything legally sensitive, use a dedicated e-signature tool.
• Do I need to install software to sign a PDF? No — browser-based tools like InkRobin work entirely in your browser with no installation required.