TextMaker Viewer is a solid alternative for MS Word Viewer
When I translate, I often use huge files for reference; these are glossaries and consistency tables that stretch on for hundreds, and sometimes thousands, of pages. Loading these files in a normal copy of Word puts a major dent in system performance. Word keeps trying to auto-save them or spell check them, and it simply freezes on every attempt, while I sit there and twiddle my thumbs.
My solution is to open these documents in a read-only program, which never tries to save or spell check them. It doesn't do anything other than simply present them.
I would usually use Microsoft's own Word Viewer for this. It worked quite well for me in the past. Since it's an old program, it wouldn't read Docx files natively, and it kept converting them to Doc. It wouldn't save the converted file, though (because it can't save). It kept on converting the file every time I opened it. Once, I converted it myself using Word and just opened the resulting Doc; it was quite smooth and fast.
That is, up until I installed Office 2010. Once I had Office 2010, Word Viewer started giving me some trouble, so I had to go in search of alternatives. What I ended up with is TextMaker Viewer, and I just might stick with it, even after MS updates Word Viewer (especially if they fix the annoyances I've listed below).
It's a simple document viewer, but it supports Docx natively, and it's fast. It has a nice tabbed interface, and once a file is loaded, page scrolling is instantaneous -- even in a file that is hundreds of pages long.
There are two major downsides to the program, though. First off, it incessantly asks you to "register it" (even though it is free). There is no way to say "stop bugging me." It just won't.
The other downside is that while search is very very fast (faster than Word Viewer, I think), there is no option to "search whole document." You can only search forwards or backwards, so you have to go to the beginning of the file every time you want to search the whole thing. I hope they do fix this in the future.