I can find out the browser version and specific capabilities using the HttpBrowserCapabilities object, but is there a way I can find the Document Mode that the browser is using
You should be able to use the Request.UserAgent
to get the string that has the capability flag in it.
Check these 2 links.
Understanding User-Agent strings
User-Agent Properties
Edit Figured I would add more detail. Basically the Trident token of the User-Agent string is the REAL version of the browser and the MSIE token is the browser mode it is using. You can easily check this out by using the first link and running fiddler to see what the HTTP headers look like.
MORE EDIT
I turn on fiddler and browse to www.yahoo.com with IE9.0 and see User-Agent: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; WOW64; Trident/5.0)
I then hit the compatibility mode button and see:
User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.1; WOW64; Trident/5.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; .NET4.0C; .NET4.0E; Zune 4.7)
See how the trident = 5.0 both times but the MSIE is 9.0 and then 7.0?
Depending on the URL you are going to there are ways to force this information. For instance on the web app I am working right now we force IE7 Compatibility mode because of some various reasons.