Changing default app for reading PDFs

1( In the Finder, select a PDF file (any PDF file will do).
2) Do a 'Get Info' on the file with the submenu or Cmd+I
3) Go to the bottom of the 'Get Info' window and expand the 'Open With' disclosure
5) Select DocuScan from the list of apps in the popup.
6) Press the 'Change All' button
7) In the Alert window press Continue..

Note: I have the latest version of Hi Sierra on my Mac.

Hope this helps.
mani