PDF file with password protection - phishing?

Hi all,

From what I thought was a legitimate source, I was sent an email attached with a password protected PDF file. The password was supposed to be my username but each time the response was 'incorrect password' and the file appeared not to open.  I found out the email was not sent by the legitimate source, so i assume it is a phishing email.  I'm now worried I might have infected my PC.  As anyone out there come across anything like this ?