A CRJ Flight Crew inbound to CLT suffered a track deviation when they programmed and initiated the UNARM ONE STAR--for which they had not been cleared. Confusion over the format and content of their PDC was cited as a contributing factor.

Narrative

Our dispatch release routed us as follows: DOOLEY5 GRD DCT UNARM DCT ADENA ADENA2. Our PDC cleared us with DOOLEY5 GRD UNARM./.KCLT We were on the UNARM ONE arrival into CLT when ATC (CLT approach) gave us a turn to 340; to begin the downwind for landing 18R. After becoming established on the downwind; ATC asked us what arrival we were given. We responded that we had been given the UNARM ONE arrival. ATC then asked us; 'Who issued that clearance?' Then we replied; by stating Atlanta. Nothing else was mentioned by ATC. We were vectored for the approach into 18R and continued to land uneventfully.After the safe completion of the flight. We later examined the PDC and what was entered in the FMS. The way that we received the PDC it was hard to tell if the clearance was; as-filed after UNARM or if it was the UNARM 1 arrival. Prior to the dispatch of the flight the crew had to swap airplanes three times. There was some pressure to get the flight out and to the destination on time. More attention to Clearances will be used in the future. I also think that ATC should not issue an as-filed clearance after the name of an intersection that is also the name of another arrival. This simple change can prevent others form making the same mistake in the future. In the future the use of ./. to say AS-FILED in a PDC is sometimes not clear when printed on the ACARS Printer. Another description might be a better fit.