The Exec key in a .desktop file accepts only one executable name (+ arguments):

The Exec key must contain a command line. A command line consists of an executable program optionally followed by one or more arguments.

So, you either:

• invoke the shell with an explicit sh -c "command_string" (where command_string = your actual commands):

   Exec=sh -c "cd /home/abc/wikidpad; python WikidPad.py"
  

or

• put your commands in a script (somewhere in your $PATH), make it executable and have the .desktop file execute the script:

  Exec=my_script
  

(or Exec=/full/path/to/my_script if the script is not in your $PATH).