Sign PDF
Adding your signature to a PDF is the standard way to sign contracts, agreements, and official forms without printing, signing by hand, and scanning. There are two distinct types: an image signature, which places a picture of your handwriting or initials on the page (quick and widely accepted for everyday purposes), and a digital certificate signature, which cryptographically binds your identity to the document (required for legally binding e-signatures in many jurisdictions). For most everyday business documents, an image signature is sufficient; for contracts where legal enforceability matters, check the requirements in your jurisdiction.
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When you'd use this
- Signing an employment contract received by email
- Countersigning a rental agreement or NDA
- Approving an internal document or sign-off form
- Adding an authorised signature to a PDF invoice before sending
- Signing a government or tax form that was sent as PDF
Before you convert
Understand image signatures vs certificate signatures
An image signature places a photo or drawn signature on the PDF page — it looks like a signature but has no cryptographic proof of who signed or when. A certificate-based digital signature (using a PKI certificate) is verifiable and tamper-evident. For legal documents where you need to prove authenticity later, a certificate-based signature or a dedicated e-signature platform (DocuSign, HelloSign) is more appropriate.
Draw your signature on a touch device for a natural look
Most browser-based signing tools let you draw with a mouse, stylus, or finger. A stylus on a phone or tablet produces a much more natural-looking signature than a mouse. Alternatively, scan your handwritten signature on paper, cut out the background, and upload it as a PNG image.
Check that the signature is positioned correctly before saving
Zoom in on the signature field area before finalising. Misplaced signatures — especially on legal documents — may require counter-parties to re-sign the document. Most tools let you drag the signature into position before committing.
Common things that don't survive conversion
- Certificate-based signatures are invalidated if the PDF is edited after signing
- Image signatures have no cryptographic validity and can be copied to other documents
- Legal enforceability varies by jurisdiction — EU eIDAS, US ESIGN, and other regulations have different requirements
- Some PDF forms are locked after signing; adding a second signature may require unlocking the document first
- Password-protected PDFs may need to be unlocked before a signature can be applied
Frequently asked questions
Is a digital signature on a PDF legally binding?
It depends on the type of signature and your jurisdiction. In the US, ESIGN and UETA make most electronic signatures legally valid for commercial contracts. In the EU, qualified electronic signatures (QES) under eIDAS have the same legal effect as handwritten signatures. A simple image signature is weaker legally than a certificate-based one — if you need provable legal validity, use a platform like DocuSign that provides an audit trail.
What is the difference between a digital signature and an electronic signature?
Electronic signature is the broad term for any electronic indication of agreement — including a typed name or image of a handwritten signature. Digital signature technically refers to a cryptographically generated signature using a certificate, which provides mathematical proof of identity and document integrity. In everyday use, the terms are often used interchangeably.
Can two people sign the same PDF?
Yes — each person signs their copy and sends it back, or you use a multi-party e-signature platform (DocuSign, HelloSign) that routes the document to signers in sequence. Adding a second image signature to a PDF yourself does not create a multi-party workflow.
How do I verify that someone else's digital signature is genuine?
In a PDF viewer like Adobe Acrobat, go to the signature panel. Certificate-based signatures show the signer's name, the certificate authority, and whether the document has been modified after signing. Image signatures cannot be verified this way — they're just pictures.
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Browse File Formats
Reference details for 53 file formats — extensions, MIME types, what opens each one, and how they convert.