Why can't I open attachments in Yahoo mail app?

[AC Question]

On both Samsung S4 mini phone and Lenovo tablet I have downloaded the Adobe acrobat app. When I tap on the pdf attachment it asks if I want to save or view. I tap "View" and the message "Cannot find application to open file" appears.
If I go to downloads on tablet and tap on the pdf attachment file it says "Can't open file"
If I use File manager and go to Download and tap on file, it opens in adobe acrobat. Is this how it should be?

 

[the tall guy]

Very strange - so it won't open unless you access it through a file manager?