A ticket is a receipt. And that in the most literal sense: A ticket is a receipt that proves that you paid for a service, and that is what allows you to be on board a train…
So to get travel expenses reimbursed (from eg. your employer) just submit the ticket. I travel a lot by train for business purposes and always just submit the tickets themselves. The only time I need a separate receipt is when I need to expense an Interrail pass. (Yes, I use Interail for business travel :-) )