Give yourself an advantage in your job applications:  put your cover letter and resume in a single PDF file, so the reviewer simply has to open one file. In your email, say what you’ve done.

As I review resumes, I realize how much easier it is to open just one file that has everything in it (including writing samples I requested).  I like the person who did it much better than I like the other people, who give me 3 files to open. 

Is that fair? Not really, except it tells me that some people really thought about the “user experience” and made it simple.  That’s the kind of forethought and solution focus I’m looking for in any job candidate. They have shown how they will behave as employees, and I like that – a lot.