'Access to files via Google search vs direct link

I was looking for some papers online and found out something weird (at least to me). When I do a search in Google I can find the paper and can access it by clicking the link that came up in my search:

Google Search

However. when I copy the link and paste it, I no longer have access to the file. It is taking me to the user credentials page https://jpm.pm-research.com/user/login:

Login Page

Can someone explain this behavior? Am I able to access file by modifying the URL of that website?



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