How to Sign a PDF Online
The free offline way is a signature overlay: draw the signature onto a copy of the PDF, then verify the text is really in the output. Tested 2 November 2026 with reportlab 5.1.0 and pypdf 6.21.4 — a 1-page sample came back as 1 page with the signature and date text intact. Clioos does not offer a signing tool. And one warning up front: an overlay is a visible mark, not a certified digital signature.
At a glance
- Clioos has no PDF signing tool. The method below runs on your own computer with free, open-source tools — no upload, no account.
- Tested: a 1-page PDF got a signature (J. Lee) and date (2 November 2026) stamp and read back as 1 page with both strings present.
- An overlay proves nothing about identity and carries no cryptographic certificate — for contracts that require proof, use a certified e-signature service.
- Browser signing tools work without installs, but your file uploads to a vendor server.
- Always sign a copy and keep the unsigned original.
Steps
- Build the overlay with reportlab: a signature line (J. Lee in the test) plus a date line (2 November 2026), placed above the signature line.
- Merge with pypdf: open the original page, merge_page the overlay onto it, write the signed PDF.
- Verify: re-open the signed file — 1 page, 1,526 bytes in the test — and confirm extract_text contains the signature and the date.
- If the signature lands in the wrong place, adjust the overlay coordinates and re-merge from the original — never stack overlays.
Worked example (tested 2 November 2026)
Test file: a 1-page sample agreement with a printed signature line. Method: reportlab 5.1.0 for the overlay, pypdf 6.21.4 for the merge.
| Step | Result |
|---|---|
| Original | 1 page, unsigned |
| Overlay added | Signature J. Lee + date 2 November 2026, on the signature line |
| Signed output | 1 page, 1,526 bytes, signature and date text both extractable |
Page count did not change (1 stayed 1), and the signature is ordinary PDF content — it renders in any reader.
Overlay vs certified signature
- Overlay (this guide): a visible mark. Anyone with the file can copy or move it. No cryptographic proof of who signed or when.
- Certified / digital signature: certificate-backed and tamper-evident — the file shows if it changed after signing. This is what banks, courts and strict counterparties usually require.
- Rule of thumb: internal approvals and informal agreements can use an overlay; anything where the other side may dispute the signature needs a certified e-signature service.
What it can't do
- No Clioos tool for this: Clioos does not offer PDF signing. The method above is the free offline route.
- No identity proof: an overlay does not verify who signed. It is weaker evidence than a certified signature.
- Locked or certified PDFs: a password-protected or already-certified PDF cannot be overlaid this way — unlock or re-issue it first.
- Not a form fill: signing does not fill form fields. Fill the form first, then sign.
- Legal weight varies: whether an overlay counts as a signature depends on jurisdiction and the counterparty. This guide is not legal advice.
Free alternatives, honestly compared
- Offline overlay: free, private, no upload — but not certified, as above.
- Browser signing tools: draw, type or upload a signature and drag it onto the page, no install — but the file uploads to a vendor server.
- Certified e-signature services: identity checks, audit trails and tamper evidence — free tiers and trials vary, full use is usually paid.
Frequently asked questions
Is it free to sign a PDF?
Yes, with the offline overlay method — free and open source. Browser tools are free up to a limit; certified services usually charge.
Is an overlay signature legally valid?
It depends on jurisdiction and on whether the other side accepts it. An overlay is weaker evidence than a certified signature. For anything disputable, use a certified service. This is not legal advice.
Will the signature show in every reader?
Yes — it is ordinary PDF content, not an annotation layer, so it renders everywhere the document does.
Can I sign a password-protected PDF?
Not with this method. Unlock it with the password first, then overlay and re-save.
Related guides: How to edit a PDF · How to merge PDF files · How to convert PDF to JPG · All guides · Tool: PDF Probe