Signing a PDF online takes a minute. What most guides skip is what the signature does to the file: it can quietly add hundreds of kilobytes, which matters when a portal caps uploads at 200 KB. We signed two test PDFs with our own PDF Signature Tool using a drawn signature, a typed one and uploaded images of different sizes, and measured the result. We also checked whether the text in the document survived. It did, and the way the signature is stored explains everything else.
How the signature tool works
The PDF Signature Tool opens your PDF in the browser. You create a signature by drawing it, typing your name in a script font, or uploading an image, place it on the page, drag it into position and resize it by its corner. When you download, the tool inserts the signature as a picture into your original PDF and saves it. Nothing is uploaded, and the rest of the document is left as it was. That is different from the Compress PDF tool, which redraws every page as an image. Here only the signature is an image.
What each kind of signature adds
We signed a one-page text invoice (2.5 KB) and a three-page photo PDF (571 KB) and recorded the size afterwards:
| Signature | Invoice (2.5 KB) | Added | Photo PDF (571 KB) |
|---|---|---|---|
| Drawn with the mouse | 5.6 KB | +3.1 KB | 574 KB |
| Typed name (script font) | 11.0 KB | +8.5 KB | 580 KB |
| Uploaded PNG, 300 × 120 px | 6.5 KB | +4.0 KB | – |
| Uploaded PNG, 1200 × 480 px | 20.0 KB | +17.5 KB | – |
| Uploaded PNG, 3000 × 1200 px | 57.5 KB | +55.1 KB | 626 KB |
| Phone photo of a signature, JPG 3000 × 1200 | 225 KB | +223 KB | 794 KB |
The added size tracks the pixel dimensions and the noise in the image you supply, not the size on the page. A clean signature at 300 pixels wide adds 4 KB; the same signature at 3000 pixels adds 55 KB; a photo of a signature on paper, which has background texture, adds 223 KB. The photo PDF shows the same increases on top of its 571 KB, so the cost is a fixed amount per signature rather than a percentage.
For a portal with a tight size limit, draw or type the signature, or crop and shrink an uploaded image to about 600 pixels wide with plain white or transparent background before you add it. The Image Resizer and Background Remover can prepare one. Our PDF compression guide explains why compressing the signed file afterwards is risky.
Does the text survive?
Yes. We counted the text items in the invoice with a PDF reader library before and after signing: 119 before and 119 after. The document is still searchable and can be copied from. This is the practical advantage of signing with a tool that adds an image to the existing file instead of rebuilding the pages.
The order that avoids problems
Our other tests showed that some PDF steps change the file in ways that affect a signature, so the order matters:
- Fill in forms first. Merging PDFs in our test dropped the form fields from 10 to 0, so fill and check any form before it is merged or signed. See the merging guide. The PDF Form Filler handles forms.
- Merge and arrange pages next, using Merge PDF, so the signature lands on its final page.
- Sign last, after pages are final. If you must make the file smaller, do it before signing, and remember that compression turns text into pictures.
- Download and open the result to check the signature position on every page that needs it.
An electronic signature is not a certificate-based one
An image of your signature placed on a PDF is an electronic signature. It is widely accepted for everyday agreements, but it is not a digital signature that cryptographically proves who signed and that nothing changed afterwards. Our tool does not create certificate-based signatures. Some documents and some countries require a particular kind of signature or a witness, and the rules differ, so confirm with whoever is asking before you rely on an image signature for anything with real legal weight.
Step by step
- Open the PDF Signature Tool and add your PDF.
- Choose Draw, Type or Upload. Drawing and typing keep the file small, and typing offers script fonts such as Dancing Script and Great Vibes. Use New initials for a page-by-page mark.
- Select Save & Place on Document, then drag the signature to the line and resize it by its corner.
- Repeat for each page or field that needs one, then select Download signed PDF.
- Open the file, check every placement and its size against your limit.
The tool works in your browser, so your document and signature stay on your device.
What we did not test
We tested Chrome with two PDFs and images we generated, so a real signature photo will differ in size. We did not test signing scanned or password-protected PDFs, how every PDF viewer displays the placed image, or whether a particular recipient accepts an image signature.
