If the file is locked by the process exclusively, it is not possible to open those files. But if the process holds only shared lock, we can open the file using c# using the following code,

FileStream objf = new FileStream(”Ouput.xls”, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);

Excel hold the shared lock on the files.

The Following is an example program to read a file,

1. using System.IO;
2. 
   
3. public static byte[] ReadFile(string filePath)
4. {
5. byte[] buffer;
6. FileStream fileStream = new FileStream(filePath, FileMode.Open, FileAccess.Read);
7. try
8. {
9. int length = (int)fileStream.Length; // get file length
10. buffer = new byte[length]; // create buffer
11. int count; // actual number of bytes read
12. int sum = 0; // total number of bytes read
13. 
    
14. // read until Read method returns 0 (end of the stream has been reached)
15. while ((count = fileStream.Read(buffer, sum, length - sum)) > 0)
16. sum += count; // sum is a buffer offset for next reading
17. }
18. finally
19. {
20. fileStream.Close();
21. }
22. return buffer;
23. }