How to add a stamp to a PDF
Last updated: 2026-07-27
Someone emails you a quote, an NDA, or a purchase order and asks you to "sign and return." The default workflow is print, sign, scan, save as PDF, attach. If you are working from home without a printer, that one page can eat an afternoon. Prepare a single signature or stamp image once and you skip the whole loop.
Start with a good source image
Sign or stamp on a clean sheet of white paper and scan it at 300 to 600 DPI in colour mode. Save as PNG, not JPG. JPEG compression scatters faint speckles along high-contrast edges, and those speckles turn into a dirty halo the moment you try to make the background transparent. PNG is lossless, so the white paper stays at a clean 255 and the edges stay crisp.
Sign five or six times on the same sheet and pick the best one; handwriting varies more than you expect, and rescanning is slower than signing again. Use a gel pen or fineliner rather than a ballpoint, which skips and scans grey.
Placing it on the page
Open your PDF in StickPDF using the 'Open PDF' button or by dragging the file into the window. Then drag your signature image onto the page where it belongs, and it drops right there. If the image is already on your clipboard, press Ctrl+V to paste it. On a phone or tablet, use the '+ Add image' button instead.
Drag the image to reposition it, grab the corner handle to resize, and click it to reveal buttons for background removal, duplicate, and delete. When the page looks right, click 'Download PDF' and you get a new merged file. Your original PDF is untouched.
Worth noting: all of this runs in your browser, so contracts and offer letters are never uploaded to a server.
Getting the size right
This is the most common giveaway that a signature was pasted in: on screen it is tempting to size for visual impact, and the result comes out two or three times larger than a real pen signature. A handwritten signature is typically 40 to 70 mm wide (1.5 to 2.75 inches); a round company seal or notary stamp is usually 20 to 40 mm across. On a Letter or A4 page, that means spanning roughly a quarter to a third of the text column, not half the page.
A quick sanity check: at 100% zoom, compare the signature height against the body text beside it. If it towers over three or four lines of type, it is too big. Sit it just above the printed signature line rather than centred on it, the way a pen rides above the rule.
Problems you will hit
- A white rectangle covers the text underneath. Your image still has its paper background. Click the image and choose 'Remove background' to make white and near-white pixels transparent. 'Restore background' undoes it if you do not like the result.
- A grey fringe survives the removal. The scanned background was not white enough. Raising scanner brightness slightly and rescanning fixes this more reliably than any amount of fiddling afterwards.
- The signature sits at a slight angle. Half a degree of rotation is visible to the eye. Straighten the source image before you place it.
- It looks fine on screen but prints blurry. The source resolution is too low; anything under 300 DPI falls apart in print.
Multi-page documents
When a contract needs initials on every page, build one image properly and then use 'Duplicate' or 'Copy' to reuse it, rather than adding the file again each time. Re-adding tends to leave initials at subtly different sizes on every page. Transparent PNGs keep their transparency when embedded, so a cleaned-up image only needs cleaning once.
About the legal side
Be clear-eyed about what this is. A signature or seal image pasted onto a PDF is a visual mark. It is not a cryptographic digital signature, and it carries none of the tamper-evidence or identity verification that a qualified electronic signature under eIDAS, or a notarised document, provides. Anyone who receives the file can lift the image out of it.
In practice, plenty of routine business documents move on visual marks alone: internal approvals, purchase orders, quotes, and delivery notes. Whether that holds up depends on your jurisdiction, the document type, and what the parties agreed. Deeds, property transfers, wills, and anything requiring notarisation generally do not qualify. If the stakes are meaningful, ask the counterparty up front, and use a certificate-based e-signature service when an image is not acceptable.
Keep the file safe
A transparent signature PNG is reusable, which is exactly the risk: anyone holding it can apply your signature to any document. Keep it off shared computers and team drives.