Electronic Signatures Are Not Just "Drawing a Signature"
Many people think an electronic signature is simply taking a photo of their signature and pasting it onto a PDF. That's only the most basic form. By legal and technical rigor, PDF signatures fall into several categories:
- Image signatures: a photo of a handwritten signature pasted on—simplest, with the weakest validity
- Digital certificate signatures: based on PKI certificates, with timestamps and tamper protection—strong validity
- Third-party signing platforms: certified through a CA authority, with the strongest legal validity
For everyday internal circulation, an image signature is enough; for formal contracts and external documents, a digital signature or third-party platform is recommended.
Image Signatures (Suitable for Internal Circulation)
Create a Signature Image
- Handwrite your signature on white paper and photograph it
- Remove the background with image processing and convert it to a transparent PNG
- Crop it to a suitable size
Paste It onto the PDF
- Open the PDF Signature Tool
- Upload the PDF and the signature image
- Drag the signature to the signing position and adjust the size
- Save and download
Tips:
- The signature image background should be transparent; otherwise it looks ugly with a white box
- The signature size should match the signature line—don't make it too large or too small
- When the signing position is the same across multiple pages, note the coordinates and batch-place them
Digital Certificate Signatures (Suitable for Formal Contracts)
A digital signature is more than pasting an image—it uses a certificate to hash-sign the document content, so any subsequent tampering will be detected.
Apply for a Certificate
- Apply for a personal/business digital certificate from a CA authority
- Some office software has built-in certificate generation (self-signed certificates, with limited validity)
Signing Steps
- Open the PDF in a tool that supports digital signatures
- Select the certificate
- Choose the signature position and appearance
- Apply the signature—the document gets tamper protection
After a digital signature, the document is marked "signed," and modifications by others will trigger a signature-invalid warning.
Legal Validity of Signatures
- Image signatures: can prove the intent to sign, but are easily denied as "I didn't sign that"
- Digital signatures: can verify the signer's identity and document integrity, with stronger validity
- Third-party signing platforms (e.g., e-Qianbo, FaDaDa): real-name authentication + timestamp + evidence preservation, with the most complete legal validity
For important contracts and external signing, use a third-party platform—don't just paste a signature image.
Common Questions
Can I Still Modify After Signing?
Modifying after a digital signature breaks the signature and triggers an invalid warning. So signing must be the last step.
Multi-person Signing Order
Multi-person signing usually flows in order—each person signs and passes it to the next. For complex situations, use a third-party platform to manage signing order.
Inaccurate Signature Position
Use a tool that supports drag-and-drop positioning—visual adjustment is more accurate than entering coordinates.
Summary
Electronic signatures come in three tiers by rigor: image, digital certificate, and third-party platform. Images are fine for internal use; for formal contracts, use a digital signature or third-party platform. Signing is always the last step—don't modify after signing. DocsAll's signature tool is suitable for image-signature placement, processed in the browser without uploading—contract privacy is secure; for formal contracts, it's recommended to add third-party platform authentication.