I want to show all the documents in the farm and ofcourse I don't want to use powershell for that as this will impact performance. I want to use something using search index. I think we can do this using data view webpart but I am not sure how to achieve the document file type and document name of all the documents in the farm?
You can set a keyword query using the Search Core Results Web Part and the Fixed Query properties.
You will need to specify a property, but I'm pretty sure I've done some simple queries like 'isDocument=true' or you can specify the file extension if desired.