The iPad-only version of the app has been discontinued and does not run on iOS 11 (due to a technical issue, not by my design).
The iPhone-only version of the app was updated to run on both iPhone and iPad. If you did not previously own the iPhone (now universal) version, you will need to purchase and download it. It from the App Store. You can find links here. (The links no longer work on desktop version of iTunes, tap on them from iPhone or iPad.)
If you were logged into iCloud on your iPad, you should be able to restore your bookmarks & highlights by going to the Settings screen (by tapping the "gear" button), selecting "iCloud Backups" and then selecting the most recent backup (listed first).
Again, apologies for the inconvenience! Please contact me if you have any questions.