File handling exceptions

If you would like to the Try-Catch approach, you could use FileNotFoundException to check if the exception was raised as specified file/path could not be found

try
{
  // Attempt Opening the file
}
catch (FileNotFoundException e)
{
  // File Not Found
}
catch(IOException e) when (e.Message.Contains($"The process cannot access the file '{filePath}' because it is being used by another process"))
{
  // File being used by another process
}
catch(IOException e) 
{
  // An I/O error occurred while opening the file (could be any other reason)
}

Futhermore, you could filter the IOException to ensure the particular error is due to the fact the file is being used by any other process.

Alternatively, you could also use File.Exists to check if the File Exists before attempting to open the file.

if(File.Exists(filePath))
{
   try
   {
     // File Exist, open the file
   }
   catch(IOException e)
   {
     // Error opening the file
   }
}
else
{
  // File do not exist
}