A drawn signature looks like a signature but proves nothing about whether the file was altered afterward. Sign with Certificate applies a real cryptographic signature that any PDF reader can verify, mathematically confirming the document hasn't changed since it was signed.
How to digitally sign pdf
- 1
Upload your PDF file
Drag it onto the upload area, or click to choose it from your device.
- 2
Select Sign with Certificate
Choose the tool, then place the visible signature stamp on the page.
- 3
Click Sign
Your file is processed on our server, which generates the certificate and applies the cryptographic signature.
- 4
Download your signed PDF
Any PDF reader can now verify the signature and confirm the file is unmodified.
Why use RealPDFTool for digitally sign pdf
Real cryptographic proof, not just a visual mark
The signature is mathematically tied to the file's exact contents at signing time.
Frequently asked questions about digitally sign pdf
What's the difference between this and Sign PDF?
Sign PDF adds a drawn, visual signature. This tool adds a real cryptographic signature that any PDF reader can verify — proving the file's contents haven't changed since signing.
Does this verify my identity?
No — it uses a self-signed certificate, which proves the document is unmodified but doesn't verify who you are the way a certificate from a paid certificate authority would.
Can I add a visible signature stamp too?
Yes, place a visible signature-style stamp on the page in addition to the underlying cryptographic signature.
Is there a file size limit?
PDFs up to 100MB are supported, since signing runs on our server.