I have the Lide 50 and if i save to PDF, it opens in Adobe reader.
Have you tried right clicking the file and use Open with to select Adobe.
From the Canonscan toolbox if I click Save then use the dropdown box to select PDF, it automatically opens in Adobe.
Also in the Canonscan toolbox the File icon has a picture icon of Adobe in it.
So it is just a case of sorting out the settings.If you do not have Adobe reader it can be downloaded from here.click here
IF that download is to big try Foxit PDF reader which can be downloaded here.click here