How to sign a PDF without printing it
You do not need to print, sign and scan a document to put your signature on it. This guide shows how to add a visible signature to a PDF in your browser, how to reuse it, and when a certificate signature is the better choice.
Worked example: signing a renewal letter
In this test we signed a fictional one-page tenancy renewal letter of 1,300 bytes. In Sign PDF we drew a signature on the pad with the mouse, selected Place signature, and moved it to the Signed line by typing its position and a width of 150 points into the object panel. The exported PDF was 3,246 bytes. The letter text could still be selected, and the signature was saved as drawn lines rather than as a picture.
We then gave that exported copy to Sign PDF with a certificate, using a self-signed test certificate made for a fictional signer. The signed file was 37,286 bytes. The tool reported that the signature matched the complete file. A separate PDF checker (poppler) agreed that the signature was valid and reported that the certificate issuer was not trusted, which is what you should expect from a self-signed certificate.
Add a visible signature
- Open Sign PDF and select or drop the PDF. The Add signature pad opens.
- Draw your signature with a mouse, trackpad, finger or stylus. Use Undo stroke or Clear drawing if you want another try.
- Select Place signature. It appears on the current page with handles for moving and resizing.
- Drag it into place, or type exact values into the x, y and width boxes in the panel on the right.
- To sign other pages, go to the page and select Add signature again.
- Select Export, then Download PDF, and open the download to check the signature sits where you expect.
Drawn, uploaded or typed
The pad gives you two ways to make a signature: draw it, or select Upload signature image and choose a PNG or JPG picture of your signature, such as a photo of it on white paper. An uploaded picture is placed as an image that you can move and resize like any other.
There is no typed signature style. To add your printed name, initials in type, or the date, use the Text tool in the toolbar and place the text next to the signature.
Reuse your signature on other documents
Open Reuse a signature on the pad and select Download reusable signature. You get a small file called redactninja-visible-signature.json; ours was 3,164 bytes. Next time, choose it under Load saved signature and select Use saved signature.
The signature is not kept in your browser or anywhere online. It exists only in the files you download. Anyone who has that file can place the same drawing, so store it like any other personal document.
What a visible signature is, and is not
A drawn or uploaded signature is part of the page content, like ink on paper. It shows that someone placed the mark. It does not prove who did it, and it does not stop anyone changing the document afterwards. The pad says this itself: "A visible signature only. This does not certify identity or digitally sign the PDF."
Many everyday letters and forms only need this kind of signature. Some do not. RedactNinja does not decide whether a signature meets a legal or organisational requirement, so check with the person or organisation asking for it.
When you need a certificate signature
Use Sign PDF with a certificate when the recipient asks for a digital signature based on a certificate, or when you need to show that the file has not changed since it was signed. It adds an invisible cryptographic signature to a separate copy of the PDF.
- Add any visible signature first and export the PDF. The certificate tool signs the file you select, not unsaved changes in the editor, and later edits would affect the signature.
- Open Sign PDF with a certificate and select the exported PDF.
- Choose your certificate (PEM, CER, CRT or DER) and your private key in PKCS#8 form (PEM, DER or KEY). Enter the key password if it has one. PFX and P12 files are not supported.
- Select Preview signing certificate and check the holder, issuer and dates.
- Tick the box confirming you are authorised to sign with this key, select Sign PDF, then Download signed PDF.
Before you send the signed PDF
Keep an unsigned copy, and do not edit, merge or compress the file after a certificate signature has been added. If you need changes, make them to the unsigned copy and sign again. You can check a signed file with Verify PDF signatures. Certificate trust, revocation and timestamps are not checked when you sign.
Your PDF, signature drawing and private key are processed in your browser on your device and are not uploaded. For a fuller explanation of the two kinds of signature, read PDF signature images and certificate signatures explained.