Then stop it! That is, unless you need the recipient to edit and send it back (but that’s another post, you should be using Google Docs).
Word or Excel files are not universally compatible. A person may have an older version of Word, Excel or Office and they won’t be able to view a file or view it the way you intended. And if you send it to a Mac person they are even more likely to have problems with it.
It is pretty easy to create PDF files of ANYTHING and to email those files instead. PDF is a univeral format that displays the original data just as it was originally created.
Mac’s have PDF support built in. For PCs EVERYONE should install a program such as CutePDF which is a printer driver. That means anytime you are looking at something you want to send to someone, be that a word doc, a spreadsheet, a webpage, an email message, a map, etc. , just select to print it using the installed CutePDF driver and out will popout a nice PDF file for you to email.
CutePDF is free, so what are you waiting for?