Oooo Yes, this is a "Adobe Reader" problem!
And that is a solution for Thumbnails: ... adobe_pdf_x64_fix
That has to work, for me it works so well!
But, for PDF preview in "Q-Dir x64" i have to do something :-)!
Oh you're so lazy adobe!
See also : ... How can I change the preview filter settings?
FAQ 59: Updated on: December 7th 2016 11:03