In your example, you would need to create something that would convert the Pages documents into a PDF. Automator has no Pages Actions. You would have to create an AppleScript to export the file in Pages.
Everything you want to "convert" to a PDF would require some ability of the app to convert to PDF and be controlled externally.
You can create a Print Plugin in Automator that will save the printed PDF to a folder of your choice. Just use a Move Finder Items action and select the folder you want to use to store the PDFs. The Print and select the action from the PDF menu. You could once just put an alias to a folder in there and it would work, but it doesn't seem to work anymore.
You can create custom shortcuts to the items in the PDF Services menu. If you made the short cut some addition to Cmd-P, like cmd-ctrl-p, you could cmd-p, then cmd-ctrl-P to save the PDF in the chosen folder.
If you wanted a drop box type action, you could use folder actions, but that would require a method to open the doc and export as PDF. That would be entirely dependent on the app that created the document, so there would be no way to create a generic "convert to PDF" action.