This method doesn't have any special restrictions in Reader, compared to Acrobat, except for the fact that you can't convert non-PDF files to PDF in Reader, obviously.
What is your full code, from where are you running it, and what is the full text of the error message you're getting?
7 0 obj
But I got this error:
NotAllowedError: security settings prevent access to this property or method
From the documentation of openDoc:
A document cannot be opened during another Doc Open. In such cases, Viewer raises a
NotAllowedError action exception, which escript passes to the user.
Thank for your help!