When creating your FileStream you should be using FileMode.Open and not FileMode.Create, i.e.
FileStream fs = new FileStream(@"" + offlinePath, FileMode.Open);
Using FileMode.Create will create a new file (overwriting the file if it already exists) while FileMode.Open is used to open an existing file.
Alternatively, you could pass the file name as a parameter when creating the StreamReader and not create a file stream at all.
using (StreamReader sr = new StreamReader(@"" + offlinePath))