concurrently access and modify the documents in asp.net

Question

Hi,
I am working with an application using ASP.NET. In my application i want to concurrently accessing and modifying the documents(files) in an application similar to googledocs. 
In the same way i want to implementing in my application. All files are stored in company server and I am not intreseted to store the files in Google docs. I will access those files from company sever not google server. 

can any one knows the code plz tell me asap. If any tools are available plz tell me.