Adding RM Documents instead of the number

I am trying to add the RM Document names to replace the numbers on our statement.

RMDTYPAL – RM Document Types:
0 – Reserved for balance carried forward records
1 – Sale / Invoice
2 – Reserved for scheduled payments
3 – Debit Memo
4 – Finance Charge
5 – Service / Repair
6 – Warranty
7 – Credit Memo
8 – Return
9 – Payment

How do I pull the name?