How to sign a PDF: signature images vs digital signatures

By the LambiPdf team · Updated 3 November 2026 · 6 min read

“Please sign and return” used to mean printing, signing with a pen and scanning. Today most people sign on screen. But “signing a PDF” can mean two very different things, and it helps to know which one a document needs.

Two kinds of signature

A signature image

This places a picture of a handwritten signature on the page. The image alone does not verify the signer’s identity or establish that the document has not changed. Whether a recipient accepts it depends on the document and their requirements; confirm those before using it. LambiPdf’s Sign tool does exactly this. It also works for company stamps and logos.

A certificate-based digital signature

This is a cryptographic seal attached to the file using a digital certificate tied to your identity. A compatible PDF reader can validate the signature and report changes, subject to certificate trust and validation settings. Some government, legal and financial processes require it, often through a specific provider or a national ID scheme. A signature image is not a substitute when this type is required, and LambiPdf does not create certificate signatures.

If you’re not sure which one is wanted, ask the sender. “Can I sign with an image of my signature?” is a normal question.

Making a clean signature image

1. Sign on plain white paper with a dark pen. A felt tip or gel pen gives a bolder line than a ballpoint.
2. Photograph it in good, even light, holding the phone flat above the paper.
3. Crop tightly around the signature. You can use LambiPdf’s image editor to crop and resize it.
4. Use a transparent background if you can. A PNG with transparency sits naturally on the page instead of as a white rectangle. Many phone photo apps can remove a background.

Store the image somewhere private. It is a copy of your signature, and you wouldn’t leave a stack of signed blank pages lying around either.

Signing with LambiPdf

1. Open the PDF and choose Sign / Stamp.
2. Add your signature image, then drag it into place and resize it to fit the signature line.
3. If the document has form fields for your name and date, fill them with Fill PDF forms.
4. Save, open the downloaded file and check the signature is on the right page and line.

Everything happens in your browser, so neither the contract nor your signature image is uploaded.

Before you send a signed document

• Read the whole document. Signing on screen makes it easy to skip to the last page.
• Check that every page needing initials or a signature has one.
• If the document is sensitive, consider sending it with a password using Protect PDF, and share the password by a different channel.
• Keep a copy of exactly what you signed.

Whether a particular signature is legally sufficient depends on the document and on where you are. When something important rides on it, such as property, employment or legal proceedings, check with the other party or a qualified adviser.

Questions people ask