Automator Combine PDF Application
If you want to custom name the combined PDF files, then add a Rename Finder Items action between the Combine PDF Pages action and the Move Finder Items action, with the Options set to checking the Show this action when the workflow runs check box. Set the Rename Finder Items action to Name Single Item and Name: Basename only to: [], where [] is and empty text box.



Note: When first added, the Rename Finder Items action shows as Rename Finder Items however, once you select Name Single Item in the first pop-up list box it changes the name of the action to Name Single Item.

The reason I suggest setting Name: Basename only to: [] is the .pdf extension is added automatically when the document is saved, so there is no need to type it.



That said, I was able to reproduce the issue of double pages when using the above workflow as an application See mu Update: note below for the explanation. Another way to do it, without running as a workflow from within Automator, is to create it as an Automator Service workflow as show below:

This is then available in Finder from the Finder > Services menu or the Services context menu when selecting PDF files and right-click or control-click the selected files.



Update: The cause of the double pages when used as an application with your original actions is because of Application receives files and folders as input, which already receives the selected files and by adding a
Get Selected Finder Items action it is passing the selected files again and hence double the number of pages. If you want to use it as an application just remove the Get Selected Finder Items action from your original workflow.