Detect file type?

if u mean find out the extension, like .dll, .jpg, .mp3, etc. then just use:
System.IO.Path.GetExtension(string path);
or
System.IO.FileInfo f = new System.IO.FileInfo("C\\:blah.txt");
return f.Extension;

there isnt a way to access the "file type" by those standerds. .exe = App file. .jpg, .bmp, .png = Image file. .mp3, .mp4, .ogg = audio file. they only way to find out the file type is by the extension, im prty sure about that.

Let's not even think about what if you're trying to examine a encrypted file (without having it decrypted by the file system for you).

The only two ways is to go by header (or footer in some cases) or by file extention. I could go create my own file type with a specific format, no header, and call it a sff. How would you expect to know what this is? It could be something like a xaml file where analysis of it (ignoring any headers) would tell you it might be a text file... or a xml file... or a xaml file...

I think you should stick to file extention, then check file types with tag information for the prescense of the proper tagging. If the file extention fails, you can check for tags. However if the tag checks fail treat it as unknown (my only slight clarification of Chris' explanation).

What is your goal in checking for file type?