Please check the browser console / network tool for any errors loading the PDF document or previewer component. Also check the server-side logs (alfresco.log/share.log/catalina.out) for any issues accessing the content. For PDF there should not be any transformations going on for preview but maybe an addon you have installed (if any) messes with that).
Also, what happens when you open the document details for that document? Does the previewer load? It probably has nothing to do with the quick share feature (the preview should fail on document details too) but it would be good to rule that out.
I think there is some issue with the new sdk or I dont know the exact issue, but any of the documents except .pdf and .txt are not previewing anywhere. Just to check, I have create a new maven plain project and ran it using command ./run.sh . It was showing me he same result.