I have a customer that would like a document named with year month then date after the document type. I have used custom format and it inputs it that order but when I use workflow to rename the file it puts it in as mm/dd/yyyy.
Try token formatting.
If your document name is "%(Document Type) - %(Date)" (e.g. "Invoice - 10/12/2017") and you want to reformat the date, then you can right-click on the Date token and click "Token Editor." This will bring up a dialog box for you to specify the date format you want.
yyyy: Year, 4 digits
MM: Month, 2 digits / MMMM: Month, alphabetic
dd: day, 2 digits
See more here.
I am retrieving the date from a field not the system date will that matter