Just be logical: on a client side, the user can only see the site through the browser. In general case, the user don't have any software supporting office files, which are proprietary. These days, there are standards for those file formats, but it does not change the situation: the users' computers don't support them.
But, on server side, it depends. You can support them. But of course, forget "I don't want to download". Obvious, isn't it?
And you cannot present office files directly, by the reason I explained above. There is a number of sites which support office files. The presentation of the content should be simulated. Usually, with HTML.
Tushar Vayangankar asked:What is Microsoft.Office.Interop, how it works?
When you install Microsoft Office, among other things, you got primary
assemblies installed in the GAC (Global Assembly Cache) of your local system. You can reference those assemblies and used them to, basically, create, open and modify Office Documents.
Also, these assemblies can be redistributed; see for example, http://www.microsoft.com/en-us/download/details.aspx?id=3508
To reference the assemblies, as they are strongly named
and installed in GAC, you need to reference them by names. So, in Visual Studio, you add a reference from the ".NET" tab of the "Add Reference" window. The assembly names are,
, and so on. Each such assembly comes in different versions, depending of the versions of Office and .NET Framework installed.
Please see, for example:
You will find such MSDN help pages on every Office product, separately.
In principle, there are 3rd-party products working with Office files, which would allow your to work without installation of Microsoft Office. If you are interested, I can advise the references, or you also can find them in available CodeProject answers.