I am working on a site where the client wants to provide links to Microsoft Word Doc/Docx files. This is probably a bad idea for a number of reasons but from an accessibility standpoint, is this a good idea and why?
Ideally the content would be rendered in the site via good ole' HTML/CSS to be SEO-friendly, though nowadays Google is already also indexing alternate file formats like PDF and Doc.
In terms of whether it's a good idea or not:
The greatest problem in distributing Word documents is that doing so assumes that all recipients have Microsoft Word. In cases where the entire audience is known, this may be an accurate assumption. For example, in an organization where Word is installed on all classroom computers, all employees do have access to Word. However, for documents with larger distribution or where users' technology is unknown, some recipients may not have Word and may be unable or unwilling to procure it, since it is not free. In contrast, most web browsers can be downloaded for free, and all of them can display HyperText Markup Language (HTML) documents; therefore, unlike a Word file, an HTML document can potentially be opened by anyone who requests it.
If and when you do get over the hurdle, and based on your metrics the software availability is not a barrier, here are some articles to ensure the formatting of the Word Documents themselves make them accessible:
Creating Accessible Word Docs From Microsoft: http://office.microsoft.com/en-ca/word-help/creating-accessible-word-documents-HA101999993.aspx
Create Accessible Word Docs From Web Aim: http://webaim.org/techniques/word/
(The latter is probably the better link to forward to your client as it contains specific screenshots and instructions.)
Ideally the best way to distribute content on the web is still through PDF if your client would like to preserve formatting (example: opening a Word Doc in a different Doc-reader will provide a varied visual experience).
Converting Web to PDF from Web Aim: http://webaim.org/techniques/acrobat/converting#word
IMO - I am not an advocate of having Word files on the Web simply because, depending on the nature of the content, you should limit provisions of the editable version of the content. It should be in a more widely accepted published format.