Can anyone tell me, how can we open multiple Action scripts at a same time in UFT 11.50?
I think the answer depends on what you are trying to do.
If you are attempting to create a test which contains multiple actions, then you can insert new actions or otherwise insert a call to external actions, such as if you have a generic login action you want to use across a series of tests.
If you are attempting to view actions from distinct tests, for example, to copy code blocks, then UFT does not support opening multiple tests. You can however open the test you wish to edit and then open the donor test>action>script file in notepad for example and copy away.