How to have two groups of molcules in one file

Dear all
my apologize for asking a simple question. I am new to Avagadro. I need to have two different groups of molecules in a view of Avagadro. I have created them separately (100 of molecule type A and 130 of type B). I cant have both of groups in a single file.
Would you plz help me?

Open one file, and choose Edit ⇒ Copy
Open the other file and choose Edit ⇒ Paste

Now you’ll have both fragments in a file and you can use the Manipulate tool to move them into place.

If you need, you may wish to choose View ⇒ Center to zoom out to see everything in one spot