The voucher allows you to use the full value of the ticket for a future booking but does not circumvent all of the penalties of the original ticket. You should probably expect any future refund of the voucher to be subject to the same cancellation penalty as taking the refund now.

There are quite a few terms applicable to these vouchers and not all tickets are eligible. It's worth reading the full T&C's towards the bottom of this link before deciding to use that option:

https://www.qatarairways.com/en/trav...her.html#Terms