I recently created a website for a publishing company, from where the visitors can download book samples in PDF format from the company's FTP server. On Windows, macOS and Android everything works perfectly, but on iPads and iPhones I receive the following message:
You do not have permission to view "book-title.pdf"
This happens either using Safari, Chrome or Firefox. Any suggestions? Thanks in advance.
I imagine that your publishing company's server must have some sort of iOS detection and that when it detects that the user is on iOS it returns that message. If that is the case and it most likely is, you should try to resolve this issue with your publishing company.
In the event that your publishing company can't fix this iOS detection issue, you could do a work around to fix it on your own end. This would entail setting up your own iOS detection script, and if iOS is detected, changing the PDF links to the same PDF on a separate server that can allow iOS users.