# PDF Digital Signature Validation

Did you ever receive a PDF document which is digitally signed? When you open this document in Adobe Acrobat Reader, you'll notice that it is validating the document by showing a very small 'green checkbox' in the top left corner. Something like this:

![Signature is valid](https://26034267-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-L9hsLHd6dIFI0WhWSM1%2F-L9hsND1A0wtos8z0w9t%2F-L9hs_BqTCyc9eyj50bG%2Fvalid-signature.png?generation=1523335736383710\&alt=media)

Ok, great, but what does it mean?

It means that this document has been 'digitally signed' or better, somebody has used '**a digital certificate**' to perform '**a signature**' on the content of a PDF document.

Hold up, what do we mean with a 'digital certificate' and where can I find them?

Simply put, a certificate can be seen as an electronic document which you can use to authenticate or digitally sign. A digital certificate contains information about an identity. You can find these certificates on EU national ID cards for example, or you can buy them from a Certificate Authority (CA), if you require legally binding signatures.

Now, how does that work? And how can I validate digitally signed PDF documents using an API?

This tutorial will explain:

* how to validate documents in Adobe Acrobat Reader.
* how to perform the same validation of digitally signed document in your own application.

For the latter, a step-by-step approach will be used. An example of an implementation is provided on Github:

<https://github.com/Trust1Team/vwapp>

The application is [available online](https://validation.t1t.be/).