How can I store cash receipts for expenses in the cash book (fuel receipts, etc.) as a file so that they are also transferred to the tax advisor?

You can store files in the cash entries. However, they will not be transmitted via DATEV. If you want a transmission via DATEV, you have to create a liability in the incoming payment.

You can find more information in our manual: 

Cashbook

Liabilities

Incoming payments