I uploaded a .pdf into dropbox and created a link to share it with others.
Then used that link to create a QR code.
When I share the link directly, all is well.
When I share the QR code, I get a message on my (android) phone: "Cannot display PDF (name_file.pfd is of invalid format)"
People will only be using the QR code on their phone's (it's a catalog for a show we are organizing), so we need something that works.