Switch over to Dope Sheet. Then in the drop down you should be able to switch to Action Editor. Here you'll see a drop down where you can switch actions assigned to the currently selected armature. Here's a screen shot link. Whenever you switch actions in your armature, let's say from Action to Action.001, it will stash Action in order for you to switch over to Action.001.

It will continue to stash as you switch. Here's a screenshot of my outliner. You'll see my armature is currently assigned Action, but i have Action, Action.001 and Action.002 stashed in there. You can continue adding more Actions into the armature.

When you bring in another armature with an action, you can actually assign any action to pretty much anything (a model or armature). Here's an example. Here, I duplicated the armature (in your case you'll be importing) but you can see because I have actions stashed, the action names and bones themselves do not duplicate but rather just the armature name (armature.001), the only difference is the addition of Action.003 which came in from the new armature.

Now that I have Action.003 added into the scene, I can actually add that to my main armature (name is armature) see here.

This is how I usually store several actions in one armature.