When posting files for people to download on your website, think primarily about your website visitors. That's the key. Think about these things:
How would you know? How could you possibly know the answer to these questions for every website visitor that has used (and will use) your website?
Also - some more things:
You can't know this either.
Another problem with using Word, besides making sure that the file will even open, is how will it look if they are not using the same exact version of Word that you used to create the program? Maybe they're on a Mac instead of a PC, too. You add so many more variables into the equation when you put a barrier like requiring Microsoft Word in the way for your website visitors to view the content you want them to view.
How many people do you think will now actually view your Word document properly and see what you're trying to tell them?
Oh, and if Firefox tries to open a .docx document, you get a bunch of junk showing up in the browser. It just doesn't work properly.
Ok, so now how many people will successfully see your document?
The best thing to do is just take these extra complications out of the equation so that you don't have confused people calling or emailing you (or worse yet, not contacting you at all and just leaving frustrated). Make your website user friendly instead of adding in anything as a possible complexity, getting in the way of the information you are providing (information they are looking for).
There are two, good possible solutions here:
First, you could just put the content on the webpage itself so that it can be seen there without any more barriers. This might not be ideal for some things as you do want them to print them out or you do need to retain the original print version. Sometimes, though, people just get a little lazy and put information that doesn't need to be in a Word document into a Word document because they printed it out earlier or something and that's "just what format it's in." They just don't want to take the time to put that same information into a web page. In that case, they're not thinking about their website visitors.
When you think about your website visitors and want to make it easy for them, then you will realize that taking an extra 10 minutes will save each user 30 seconds or more of time (since they first have to download it and open Word, etc. etc.). If 100 people need to view that document, then you are using 50 minutes or more of other people's time because you didn't want to spend 5-10 minutes of your own time. That's what it comes down to.
Second, if you need to preserve the format of that document, then make a PDF file instead. It's compatible across platforms (operating systems) and keeps your document looking how you meant it to look. Most people have the Adobe Acrobat Reader installed on their computer. Their computer either came with it installed or they've already needed that free program in the past and have taken the few minutes it takes to install it. You're not requiring them to have your same version of Word or anything like that. It's called a "PDF" for "Portable Document Format." It was made exactly for this reason - for files to look correctly and be portable across operating systems and computers.
If you are using an Apple Mac, then you have it already. Just print to PDF from any program.
If you are using Windows, then you might not have the ability to print to PDF out of the box. You may need to install some software. There are a few out there. You could buy Adobe Acrobat. That's one option. A free PDF maker that we have used is at: PDF995.com. Just follow the instructions there the install it. Once it's installed, you just print to PDF from any program like Word. It shows up as a printer. Once you choose that printer, it'll ask you where to save the file (it doesn't print it to your printer at that point).
Remember that for any file you're putting on your website, you want to make sure you name it properly. The general rule is to stick to alphanumeric characters (a-z, 0-9) and either a dash or underscore for spaces (so, no spaces in the file name). You definitely don't want any kind of punctuation like question marks, apostrophes or ampersands in the file name.