Hello @marek,
Yes, that is possible to do in the developer account, but keep in mind that the developer environment has its limitations and to use the account for your business its purpose is only for testing/developing your integration. A production account would be needed to send documents to your customers.
You can follow the steps here to create a developer account.
To work with our C# SDK, you’ll find all the details you need on this page.
And last, but not least, you can find here information on how to implement the identity verification. Please note that you’ll find samples in C# in this very same page.
If during the developing of your application you get stuck or have issues when using our tools/documentation, please open a case with the Developer Support team and it will be a pleasure to help.
Best regards,
Leandro Reis