C:\Desktop\
is not the path to the desktop folder, and
C:\Temp\
is not the path to the temp folder. The real paths are within your user profile folder.
You can get the path to the temp folder with:
System.IO.Path.GetTempPath()
You can get the path to the desktop folder with:
Environment.GetFolderPath(Environment.SpecialFolder.DesktopDirectory)
So, to save the file on your desktop, you would use:
string destinationFilePath = Path.Combine(
Environment.GetFolderPath(Environment.SpecialFolder.DesktopDirectory),
"new.doc");
In either case, the first parameter to your
CreateWordDocument
function needs to be the real path of the existing file you want to open. If you specify a path that doesn't exist, you'll get your (misspelled) error message.