HD/PM found on a DR-15CS Sales and Use Tax Return form means Hand Delivered / Postmarked - this is a date that the department fills in once a return is received.
Here's a line-by-line instructions for DR-15CS from Florida Department of Revenue.
For more info, contact:
Florida Department of Revenue
5050 W. Tennessee Street
Tallahassee
FL 32399-0120
T: 800-352-3671 (Tax Information and Assistance)
To download forms and publication from Florida Department of Revenue's website, click here.
TIP: TurboTax shares 5 Hidden Ways to Boost Your Tax Refund.