How Do I use the "Press a Button" Action?

Keyboard Maestro 8.0.4 “For Each” Action

From the Engine log:-

2017-12-28 11:44:32 Press Button “Save” failed to find button.
2017-12-28 11:44:32 Press Button “Save” failed to find button. Macro “Quark open file - intending to export each document to pdf” cancelled (while executing Press Button “Save”).

I am stuck, unable to get the Quark XPress dialogue to Save - any help would be appreciated.

I don't have QuarkXPress installed, so it's hard to say for sure what could be going wrong without more screenshots, but I'm guessing that it's trying to press the Save button before each file is finished opening and ready to be exported. What happens if you add another Pause or Pause Until action after the Open %Variable%Path% action to ensure the file is finished opening before the macro proceeds? I don't know how well this would work since I don't know how QuarkXPress operates, but presumably, you could try something like this to ensure that the front window is the newly opened document:

Since your issue/question seems to deal more with the Press a Button action (KM Wiki) than with the For Each Action, I have retitled your topic as follows:

FROM: Keyboard Maestro 8.0.4 “For Each” Action
TO: How Do I use the "Press a Button" Action?

This will help others find and help you better, as well as future readers who may have a similar issue.

If @gglick's suggestion does not solve your issue, then please post some screenshots of the region where you want the button to be pressed.