I have seen this in more than enough resume that now it's a rule that one must follow if he/she wants to receive an interview call by sending a resume to a requirement.
Send your resume in doc format. When a resume is asked. Send it in the most used format for resume. The word doc format. Not in pdf or any other fancy stuff.
In PDF it might look good or it's un modifiable. But at the same time, it's going against the filing or the usual HR's program's or macros.
Most of the HR systems are geared and automated to filter and find the relevant resumes out of the thousands they receive. And if your résumé isn't in the standard format and file type, it will be skipped. They are not going to customise their systems because of one resume.
So until the time, PDF resumes are a norm, stick to the standard doc format, you will double your chances of getting a call for interview!!