Although modern computers are getting much better at and translation programs are getting more sophisticated, attaching a file to an e-mail message and making sure the recipient can actually read it is still a risky proposition on the Internet. I have found that you stand the best chance of successfully transferring a document if you do it this way:
This will work for most platforms and most word processing and e-mail programs. Some 16-bit (Windows 3.1) word processors will have trouble. Note that even though all Mac word processors for years and Windows 95 (32-bit) word processors (for as long as they've been around) can handle long, complicated, space-infested names on *the same machine that created them*, when you transfer files across the Internet, you're bound to hit a machine that changes the name somehow--truncates, abridges, changes to caps, etc. etc. So I advise using 8.3
This process will result in retention of most formatting--bold, tabs, italics, different fonts and font sizes, etc. It does not do the greatest job on tables and other more complicated formatting, especially cross-platform. If the recipient machine doesn't have the same fonts, some weird substitutions may take place (especially for unusual characters). I make no claims whatsoever about embedded graphics, etc. And this advice is not about spread sheet programs, data base file reports, desk top publisher layouts, etc. Only word processing files.
An alternative, if content is your major consideration, is to ignore formatting and transfer the file as a text file (Save As text) or just copy and paste it into the email document. This _always_ works.
Another alternative is to coordinate with your recipient(s) to determine what word processing program and version they are using and Save As to match. Note that Microsoft Word (and Office) don't degrade very gracefully. That is, a version of Word or Office that is one version behind cannot read the later version well at all and *sometimes* the new version can't save backwards. This is called progress. That's why RTF is your friend.
Another hint. Often when you get a file and manage to get it open, it all looks like gibberish. If you scroll down through the (maybe 20 or more) pages of junk, the content of the document is usually there in text format. (Often along with the last 3 or 4 versions that the author was contemplating--a chance to examine the inner workings of a colleague's mind???)
One final note. The most recent e-mail programs incorporate web-and-word-processing-style formatting within the message, so web addresses you send are active, columns line up, text can be colored, bolded, etc. Whether all this cool stuff still looks cool to the recipient depends *totally* on what e-mail program they are using, NOT what you send. So my advice is don't do it.