using (TextReader reader = new StreamReader(File.OpenRead(Path.Combine(client._WorkLogFileLoc, "dump.txt")))) {
//do stuff
}
Path.Combine(client._WorkLogFileLoc, "dump.txt")
Path.Combine("D:\some\path\to\folder", "dump.txt")
, что даст:"D:\some\path\to\folder\dump.txt"