The built-in Preview has the ability to bookmark PDF's, so you could combine Preview with Apple Script or Automator to automatize it. I'll clarify this approach a bit. Say, you want to bookmark the current page of the PDF whenever you say "bookmark this". Since the dictation part is irrelevant, I'm going to explain a bit about the bookmark-part. The first thing you want to do is go into automator and search for "execute Apple Script", like this (yes, it's in Dutch). It'll appear in the column on the right. Now it's time to enter the script. I've already written this script for you. on run {input, parameters} tell application "Preview" to activate tell application "System Events" key code 2 using {command down} end tell return input end run You should now have this. This script activates Preview (brings it to the foreground), and executes "Command D" on the keyboard. You can test if it works by running it with the play button. You can now assign any activator/sensor/event you want to it to make the script run. Good luck, and enjoy automatizing with this cool tool!
More about Preview in the “Advanced Features” section below.