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Digital Signatures Explained

by Hung Nguyen

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Smallpdf can help you create a digital signature and digitally sign your documents within minutes. You can also request verifiable signatures.

Smallpdf is the most popular online PDF software. We offer a standard electronic signing tool for free users, and digital signing for anyone with a Pro subscription. We’ll explain both options, along with how to request signatures below.

How to Create a Digital Signature Online

  1. First, go to our eSign tool.

  2. Upload the document you wish to sign.

  3. Click ‘Create signature’ and create your signature.

  4. Drag and drop the signature onto the document.

  5. Click ‘Finish and Sign’ to sign and download your file.


Create a digital signature and sign your document within seconds!

You can use our eSign tool to sign any PDF document. If you have electronic documents in other formats, you can convert them to PDF, before sealing them with a digital signature.

To streamline the digital signing process—you may create online signatures on PCs, mobile devices, or even tablets—via the link above.

How to Request a Verifiable Digital Signature

  1. Open your file with our eSign tool.

  2. Click ‘Add Signer.’

  3. Fill out the signer’s name and email address.

  4. Review and send the document for signing.

Smallpdf will then send your recipients a signature request. After the last person has signed the document, Smallpdf will seal the document with digital signature.

We will also keep your digital document online for 14 days, and will also send reminder emails to notify everyone to download the final version of the document.


How to request a digital signature from someone else (via email).

What is a Digital Signature?


A digital signature is a cryptographic process where a large number is calculated based on the document's contents and the attached certificate. The certificate contains the name of the signer (in our case, Smallpdf GmbH). The number that is calculated for the document can be verified with many PDF readers/software.

The digital signature can only be matched and verified if the document's content is unchanged since the signature was applied and the certificate is valid.

Once you sign a document with Smallpdf, recipients will still be able to fill forms, sign, and comment on the document—without invalidating the signature.

The Embedded Timestamp of Digital Signatures


In addition to our digital signature, we also add a timestamp that is also signed and cannot be forged. The timestamp records the exact time when a user places the signature on the document. For Smallpdf users, this is when Smallpdf processes the file online.


Signing on mobile devices is becoming the norm in digital workplaces.

How Do Smallpdf Digital Signatures Work?


When you sign a document using our tool, we provide an Advanced Electronic Signature that includes an LTV- (Long Term Validation-) enabled timestamp. Specifically, we use a certificate issued to us, Smallpdf GmbH, by a Swiss Trust Service Provider, SwissSign, to put a digital signature on your document.

You can view the digital signature’s properties with most PDF readers, which should display the validity summary, containing:

  • whether the signature is valid

  • the time of signing

  • the name of the signer and whether their identity is valid

  • whether it’s been modified since the time of signing

  • There should also be a ‘Signer Info’ section, where you can display our certificate. It should display our company name, the validity length of our digital signatures, and the name of the issuer of our digital signature—SwissSign CH.

There is also a ‘Details’ tab to show further technical information about our certificate. It should include the authority info access, authority key identifier, certificate policies, CRL distribution points, key usage, SHA1 digest of public key, serial number, signature algorithm, subject key identifier, etc.


How to check the validity of a digital signature.

Free Digital Signatures


If you would like to test out the eSign tool, you can create an electronic signature (that isn’t legally binding) right away, for free. It’s always best to check in with your local laws on the legality of electronic and digital signatures in your country.

To apply the cryptographic signing, you can sign up for a free two-week trial to Smallpdf Pro. We will also remove all ads, store your online signatures for later use, and enable access to 20 other useful PDF tools.

Hung Nguyen
Hung Nguyen
Senior Growth Marketing Manager @Smallpdf