If an employer does not state what they want as a format, and you cannot find out by calling, attach a MS Word, PDF and text as well as paste the text in the body of email. Make a note in cover letter to give them a heads up. Some companies have software that cuts attachments off without telling you. That means you sent nothing!
A lot of jobseekers don't realize the need to have their resume in different formats other than a Microsoft Word Document. Saving your word document to a PDF file prevents the resume from changing once received by the employer, if they allow an attachment. You can download the PDF converter at PDF995.com. Simply download the software and then you can open your document and file, print, and ok (not file, save as). I made the mistake of trying file, save as, and was frustrated that PDF wasn't in the drop down menu, so make sure to use print instead (even if you don't have a printer, it will end up saving the file for you, it's weird, but it works).
If the employer does not specify what format they want or allow, it's always safe to create and paste a plain text document in Word Pad. A plain text document will also be safe from changing into odd characters on the receiving end, such as a bullet changing into a quesiton mark! Who wants that?
To make a plain text document:
Simply open your Microsoft Word (or other document), copy and paste into the WordPad (located in start menu, then assessories). Then take out any formatting such as underlining, bullets, italics. You can use astericks or any keys on your keyboard to replace formatting. Then file, save as: text (not rich text). Once this is complete, you can use this anytime you apply online or email. It's safe to just paste it into the body of the email, along with your cover letter, separated by astericks. This is referred to as an "electronic" resume.