There are so many file types, and the web is incredibly accommodating. For each program you use to develop new information for your website there is a software application that allows you to publish that file on the web.
Portable Document Files (pdf), Word Documents (.doc) and many others are being integrated into standard site designs. Flash is often used to enhance the site with some pizzazz, but in each case the truth is just because you CAN put those files into your site design doesnt mean you SHOULD put those file types into your site design.
For the purposes of Search Engine Optimization (SEO) the greater you can rely on text the better your site will perform in site rankings.
You see, the trouble with these files is most search engine spiders do not recognize them because they are not text files. There are search engines that have become adept at indexing these files, but the majority of search engines do not recognize this content at all.
If you find yourself concerned with SEO techniques and their impact on site rankings then it may be worth your while to visit with your site developer to determine if there are areas where a .doc or .pdf...