sumatra_PDF_sync.ahk
This is one way to synchronize scrolling between two PDF files open in SumatraPDF when not using tabs (Settings | Options - Adavanced) and two SumartraPDF windows are open. This was adapted from a script found in a StackExchange post from ivanatpr dated 12/21/2011.
The right arrow key navigates to the next page in both windows. The left arrow key navigates to the previous page.
If you use Windows Spy (packaged with AutoHotKey), you can identify the ahk_class specific to your PDF viewer and edit the script.