Having received thousands of resumes in e-mail, I would recommend using PDF as a universal format. Some companies do not accept Word attachments because of potential macro viruses, even though the .doc format is near universal. On one hand, RTF files can be large and bulky but they can also be opened even if all the recipient has is WordPad. On the other hand, PDF files can become large and cumbersome if you include a lot of graphics, fonts or colors. If you keep your resume simple, the resulting PDF file shouldn't exceed 100kb for a 3 page resume.