Signing a PDF electronically: what to know before clicking

You receive a contract to sign as PDF. Three options:

1. Print it, sign with a pen, scan, send back
2. Open the PDF, draw a line with the mouse, export
3. Use a qualified signature platform like DocuSign / Yousign

All three are "valid," but their legal value varies enormously. Here's what to understand before clicking.

The eIDAS regulation defines 3 levels

Since 2014, the European Union harmonizes electronic signatures via eIDAS (Electronic IDentification, Authentication and trust Services). Three levels, three uses.

1. Simple electronic signature (SES)

This is what you do when you draw your signature with mouse or touchscreen in a PDF.

Characteristics:

• No formal signer identity verification
• No reliable cryptographic timestamp
• The PDF itself can be modified after signing

Legal value: recognized by eIDAS, but weakly proves that you signed, or when. Before a court, the judge evaluates case-by-case.

Appropriate use:

• Quotes and low-value purchase orders
• Internal acknowledgments
• Non-contractually binding documents

Typical tool: PDFly, macOS Preview, Adobe Reader free.

2. Advanced electronic signature (AES)

Adds three requirements:

• Signer identification uniquely linked to the signature
• Detection of any subsequent modification of the document
• Exclusive control over the creation data (private key)

How that translates: the signature includes a digital certificate (X.509) issued by a recognized authority. The PDF is encrypted such that any modification after signing invalidates the signature.

Legal value: strong. Before a court, the advanced signature enjoys a presumption of reliability.

Appropriate use:

• Commercial contracts between businesses
• Internal conventions (HR, compliance)
• Documents engaging moderate sums (€10K to €100K)

Typical tool: Adobe Sign, certificate-equipped HR platforms (Yousign Standard, DocuSign Standard).

3. Qualified electronic signature (QES)

The maximum eIDAS level. Strictly equivalent to a handwritten signature before the law.

Requirements:

• Everything in the advanced signature
• Plus a qualified signature creation device (QSCD): smart card, cryptographic USB token, or certified mobile app
• Plus a qualified certificate issued by a qualified trust service provider (QTSP)

In practice, the signer must identify themselves via a verified device (videoconference + ID, Belgian eID, ID Austria, etc.).

Legal value: equivalent to handwritten signature throughout the EU. The court doesn't have to "recognize" it — it imposes itself.

Appropriate use:

• Notarial deeds
• High-stakes contracts (company sale, real estate)
• Public tender submissions
• Tax documents engaging the company

Typical tool: Yousign Qualified, Adobe Sign Qualified, banking services with eID.

What PDFly does (and doesn't)

PDFly offers simple signature (SES): you draw your signature in the browser, we embed it in the PDF, you download the result.

When to use it:

• Returning a non-binding quote
• Stamping an acknowledgment
• Co-signing meeting notes
• Signing internal paperwork (non-binding HR convention, parental authorization, etc.)

When to use something else:

• Significant commercial contract → AES (Yousign, DocuSign)
• Notarial deed → QES (notary or qualified signature)
• Public tender submission → QES

PDFly doesn't (yet) offer AES/QES because that requires a partnership with a European QTSP. It's on the roadmap but not urgent: for 95% of daily signatures, SES is enough.

How to sign a PDF simply on PDFly

1. Go to pdfly.eu/en/tools/sign-pdf
2. Drop your PDF
3. Choose "Draw" (free-hand), "Type" (script-like), or "Import an image" (your scanned signature)
4. Click on the page to position the signature where you want
5. Download the signed PDF

Everything happens in your browser. The PDF never gets sent to our servers. Neither does your signature.

Common legal pitfalls

"A scanned signature has the same value as a handwritten one"

False. A scanned image of a handwritten signature, pasted on a PDF, is technically less reliable than a mouse-drawn signature: an image can be easily copy-pasted. Both are at the same eIDAS level (weakly probative for SES), but judges are even less comfortable with a pure scanned image.

"DocuSign guarantees legal value"

Not automatically. DocuSign offers SES, AES, and QES depending on the plan. The standard signature (most common) is AES level, sometimes SES depending on options. For deeds requiring QES, you must explicitly choose that option (and pay more).

"A handwritten signature printed then scanned is worth less than an electronic one"

True in theory, false in practice. Before French courts, a scanned handwritten signature is broadly recognized by habit, while a simple electronic signature is more contested. It's cultural, not legal.

"A signed PDF can be modified invisibly"

Variable by level:

• SES: yes, modifications possible invisibly (except for visual verification)
• AES/QES: no, any post-signature modification is detectable and invalidates the signature

Verifying a signature is valid

For advanced and qualified signatures, several tools enable verification:

• Adobe Reader: opens the PDF, the "Signatures" panel indicates level and validity
• EU Commission DSS Demo: https://ec.europa.eu/cefdigital/DSS/webapp-demo/ — verifies any eIDAS-signed PDF
• veraPDF: verifies if the signature is PDF-standard compliant

For simple SES: no cryptographic verification possible — it's just an embedded image.

In summary

Choosing the right signature level is a matter of risk fit:

To sign a PDF quickly and freely at SES level — quotes, internal conventions, authorizations — use PDFly, 100% in browser, no signup.

For high-stakes contracts, level up via a dedicated platform. The cost of an AES is marginal (~€5/signature) vs the risk of litigation.