Access a page after entering one of multiple codes

Hello,
for my next project I want to embed an PDF file on a locked site which is only accessable with the help of a password.
Because we want to send out a few passwords or rather “codes” through flyers (our marketing stuff), we want to be able to have a box on our frontpage with a button that whenever you type in a code from that flyer and press the button, if the code is correct, you’ll be sent to the page with the PDF.
BUT if you get sent the link directly to the PDF, without entering the code, the page should be blocked.
Also there should be a way to “read” how many people used a specific code so we know which people from where (from our marketing) accessed our PDF.

• This topic was modified 3 years, 1 month ago by Jan Dembowski. Reason: Moved to Fixing WordPress, this is not an Developing with WordPress topic