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Document security

Password protection vs digital signature for a PDF

By DeckleUpdated

A password controls who can open a PDF; a digital signature shows who signed it and whether it has changed since. Use a password to keep a document private on its way to the recipient. Use a digital signature when the recipient needs to trust that the document came from you and has not been altered. They solve different problems, and a document can have both. Deckle adds passwords with Password protect PDF; it does not create digital signatures.

Password protect PDF

Three different privacy tasks

Password

Controls access

Metadata

Document properties

Redaction

Selected page content

Choose the change; inspect the saved copy

Conceptual comparison · access, properties and content require separate checks. No single task certifies complete privacy.

Password vs digital signature

Password protection Digital signature
Answers Who can read this? Who sent this, and has it changed?
How it works Encrypts the file with a key derived from the password Attaches a cryptographic signature tied to the signer's certificate
Recipient needs The password A reader that validates signatures, such as Acrobat Reader
Keeps content private Yes No; anyone can read a signed file
Shows tampering No Yes; changes after signing show as an invalid or modified signature
Identifies the sender No Yes, through the certificate
Typical use Payslips, statements, medical letters Contracts, invoices, certificates, official forms

A signature image is not a digital signature

A scanned or drawn signature placed on a page is a picture. It shows a name; it proves nothing about who placed it, and it can be copied to another document. A digital signature is cryptographic data inside the file, created with a certificate, and validated by the reader. Many e-signature services add both: a visible signature image and a digital signature behind it.

When to use a password

  • The document is private and the risk is someone else reading it.
  • The recipient already knows it comes from you, such as a statement from your accountant.
  • No one needs to prove later who issued the document.

How to add one with Deckle:

  1. Open Password protect PDF and choose your PDF, or drop it onto the page.
  2. Enter a password of at least six characters in Password and Confirm password.
  3. Choose Protect this PDF and download the copy.
  4. Send the password by a different route from the file.

When to use a digital signature

  • The recipient must be able to rely on the document as yours: a signed contract, an approved invoice, a certificate.
  • Someone may need to check later that nothing was changed.
  • A regulator, court or counterparty requires it.

Use a signing app or service, such as Adobe Acrobat's certificate-based signing or an e-signature platform. Sign the final version, after every other change.

When to use both

Adding encryption to a file that is already signed rewrites it, and the signature on the protected copy will no longer validate. If both are needed, use one app that can both sign and encrypt and follow its order, or send the signed file through a protected channel instead of adding a password. Why a PDF signature is invalid after editing explains what breaks a signature.

Tips

  • Keep signed originals unchanged. Any rewrite, including adding a password, merging or rotating, invalidates the signature on the new copy.
  • Clean before signing. Remove metadata with Remove PDF metadata before the document is signed, not after.
  • Check the signature panel. Acrobat Reader shows whether a signature is valid, who signed and whether the file changed.
  • Ask the signer, not an editor, for changes. In Acrobat, a sole signer can clear their own signature and edit; with several signers, Adobe's advice is to ask for the unsigned original.
  • Do not treat a typed name as a signature for anything that must hold up later.

Frequently asked questions

Does a password prove who sent a PDF?

No. Anyone with the password can open the file, and anyone can create a protected PDF. Only a digital signature identifies the signer.

Does a digital signature make a PDF private?

No. A signed PDF can be read by anyone who has it. Add privacy through a password or a protected channel.

Can Deckle sign a PDF?

No. Deckle does not create or validate digital signatures. Its tools rewrite files, which also means they do not keep an existing signature valid.

Will adding a password break a digital signature?

If a separate tool adds the password after signing, yes: the file is rewritten and the signature no longer validates. Keep the signed original.

Related tools

Sources