You can send any file which is on your PC (or on removable media, such as a CD, floppy disk or media card) as an attachment.
Unlike image files, which generally open automatically on the recipient's PC, the recipient will need to open the file. This is usually done by double-clicking on the name of the attachment.
Obviously, the recipient must have suitable software on their PC. It would be no use, for example, sending a file created in Excel if the recipient didn't have Excel, or a compatible program, on their PC. There shouldn't be any problem sending a Word file because almost everyone has Word, or a compatible program such as Open Office, on their computer.
Exactly how you add the attachment to your e-mail will depend upon the e-mail client (or web-based e-mail service) that you are using. If it's Outlook Express, simply go to Insert > File Attachment. Navigate to the location of the relevant file and double-click on it.
Chris