[Hamid]

This is the code:

% Generate a Robolink object RL. This object interfaces with RoboDK.

RL = Robolink;

% Get the library path
path = RL.getParam('PATH_LIBRARY');

and I get this error:

No appropriate method, property, or field 'getParam' for class 'Robolink'.

[RoboDK]

Assuming that you are using Matlab, you must make sure that the following files are in the Matlab path:
Robolink.m
Robolinkitem.m

You will find these files in C:/RoboDK/Matlab/ if you are using windows. Follow these steps to add that folder to the Matlab path:
1-Select "Set path" in the Home tab
2-Select "Add folder"
3-Provide C:/RoboDK/Matlab/
4-Select "Save"