Signing a PDF With an Image Signature: How It Works and What It Is Not

Plenty of everyday paperwork only needs your name on it: a signed-off timesheet, a permission slip, an internal approval, a form you agreed to. Printing, signing and scanning takes ten minutes. Placing a picture of your signature on the PDF takes one. Our e-Sign PDF tool does exactly that, and this guide explains how to use it properly, what we found when we tested it with real files, and where it stops being the right tool.

Before anything else, the most important point: a drawn or uploaded image signature is not a certified digital signature. It is a picture placed on a page. It does not use a certificate, it cannot prove who placed it, and it does not detect later edits. The tool itself says this in a notice at the top of the page, and we cover the details in a section below.

What the tool does and does not do

You give it a signature image and a PDF. It draws the image onto the page you choose, at the position and size you choose, and saves a new PDF. That is all. We opened the signed files and checked:

• The signature is added as an ordinary picture on the page. The file has no signature field and no certificate data.
• The text of the document is untouched; text extraction from the signed page still returned all 2,334 characters.
• The result is not locked. Anyone can still edit, copy or remove things from the PDF with ordinary PDF software.

The tool offers two ways to create the signature: Draw and Upload Image. There is no typed-name option, so if you want a typed signature, you will need to make an image of it yourself first and upload it.

Step by step

1. Create your signature

1. On Draw, sign inside the box with a mouse, finger or stylus. Use the Pen color picker (default dark blue) if you want another colour, and Clear to start over.
2. Or choose Upload Image and pick a PNG or JPG of your signature, such as a photo of a signature on white paper. The tool removes the light background and shows the result over a checkerboard so you can see what is transparent.
3. Click Use This Signature. The button stays disabled until you have drawn something or uploaded an image.

2. Place it on the PDF

1. Drop your PDF onto the second step. One file at a time.
2. The tool opens the last page by default, since that is where signatures usually go. Change Page number to sign another page.
3. Use Signature size (10 to 60, as a share of the page width) to scale it, then drag the signature on the page preview to the exact spot.
4. Click Apply Signature. You will see "Your signature has been applied to page 3" (or whichever page), then click Download Signed PDF. The file is saved with -signed added to its name.

Getting a good-looking result

• Draw big and bold. The pen is a fixed thin line (3 pixels on a 600 x 200 canvas). At the default size, a drawn signature came out small and light on a letter-size page. Increase the size slider, or sign across most of the box.
• The transparent margin counts. The whole canvas is the image, including the empty space around your writing, so the visible signature is smaller than the slider suggests. Draw close to the edges.
• Photograph signatures on plain white paper in even light, dark ink, no shadows. Crop to the signature before uploading.
• Keep it above the line. Drag so the bottom of the signature sits just over the signature line. In our test, a signature placed this way landed on the line in the saved PDF, within a few points of where the preview showed it.

How the background removal slider behaves

When you upload an image, Background removal sensitivity (0 to 100, default 50) controls how light pixels become transparent. We uploaded a signature photographed on slightly off-white paper and measured the result at several values:

Sensitivity   Result
0             nothing removed: the whole photo stays opaque
25 to 75      paper turns nearly transparent; ink stays solid
100           everything becomes partly transparent, including the ink

The hint on the page says to raise it if a light background still shows and lower it if parts of the signature disappear. In practice, leave it near the default and only adjust it if you see a faint box or missing strokes in the checkerboard preview. Light paper is never made fully transparent, only very faint, so a clean white background gives the best result.

Problems we found, and workarounds

• Rotated pages. On a page that has a 90 degree rotation setting (common with scanned landscape pages), the signature came out turned sideways on the saved page. Workaround: rotate the page upright first with our Rotate PDF tool, then sign.
• Pages with a crop box. On a page whose visible area is smaller than its full page size, the signature was saved noticeably down and to the left of where we dropped it in the preview. Always check the downloaded PDF, not just the preview. If the position is off, move the signature and apply again.
• PDFs with editing restrictions. A PDF protected only by an owner password (it opens without asking for a password, but forbids editing) loaded and previewed fine, then failed at the end with "Failed to apply the signature to this PDF. Please try again." Remove the restrictions first if you are allowed to.
• PDFs that need a password to open. You get "Failed to read this PDF — it may be corrupted or password-protected." The tool has no password field; use our Unlock PDF tool if you know the password.
• Not a PDF. "Please select a valid PDF file."

Why this is not a certified digital signature

People use "electronic signature" and "digital signature" as if they meant the same thing. They do not.

• An electronic signature is any electronic mark showing intent to sign: a typed name, a ticked box, a drawn squiggle. What you make with this tool is a very simple version of that.
• A digital signature uses a certificate and a private key to bind your identity to the exact content of the document. Anyone can verify who signed it, and the signature breaks if the content changes afterwards. This tool does not create one.

The practical difference: someone could copy your signature image out of the PDF and paste it into another document, and nothing in the file can show that it happened. Nothing in the saved PDF ties it to a time, a device or an identity.

That does not make image signatures useless. Many internal approvals, school forms and informal agreements are fine with a visual signature, and electronic signatures can be valid in many places under laws such as the US ESIGN Act and the EU eIDAS regulation. But what counts as enough depends on the type of document and the country, and some documents require a specific method. For contracts, property, employment, financial or regulated paperwork, ask the other party or a lawyer what they accept, and use a certified e-signature service if they require one. This guide is general information, not legal advice.

Where your signature and file go

Nowhere. We watched the network requests while signing test PDFs. Beyond loading the page and its JavaScript libraries (pdf-lib and PDF.js, from a public CDN), there were no requests carrying the PDF or the signature. Everything is processed in the page. Two practical habits are still worth keeping: your signature image is a reusable asset, so do not leave it in shared folders; and share the signed PDF only with the people who need it, perhaps with a password using Protect PDF.

Quick answers

Can I sign more than one page? Not in one pass. Download the signed file, load it again and sign the next page. Each pass adds one signature.

Can I undo a signature after downloading? The tool does not edit your original. Keep the unsigned PDF so you can start over.

Is the signature saved for next time? No. The tool keeps it only while the page is open, so you have to draw or upload it again on your next visit.

Does it add the date or name? No, only the image. Add a date by hand to the document before signing if you need one.