Write an article based on this "Purchase Moon+ Reader Pro. Tap the ☰ menu in Moon+ Reader Pro. Tap Options. Tap the gear  next to the service you want to use. Sign in to Google Drive or Dropbox using your existing account. Enable reading position syncing."
You'll need the paid version of Moon+ in order to link your Dropbox or Drive account. Once linked, any e-books that you add to your cloud storage will automatically sync with Moon+ reader. To buy Moon+ Reader Pro, tap the ☰ at the top-left corner, tap About at the bottom, and then tap Buy Pro Version. Follow the on-screen instructions to make your purchase. It's the three horizontal lines at the top-left corner of the screen. It's at the bottom of the menu. Once you choose your service, you'll be prompted to sign in with your account. Once you're logged in, the accounts will be linked. This feature allows you to save your position in the book to Google Drive or Dropbox so you can resume from the same position on another phone or tablet:  Go to My Shelf. Tap the book you want to sync. Tap the center of the screen to view the controls. Tap the ⁝ menu at the top-right corner. Scroll down and tap "Sync reading positions" next to the service you want to use. Tap anywhere outside of the window to save your changes.