I have been advised that if you don't have an Adobe Acrobat license then you cannot log into Adobe Acrobat Pro and have it function as Adobe Reader. You need to use the Adobe Reader product.

The website https://helpx.adobe.com/au/acrobat/kb/acrobat-dc-downloads.html currently suggests that you should be able to log into Adobe Acrobat Pro and have it operate as Adobe Reader.

My suggestion is to update the website so that it is clearer that you must be licensed with Adobe Acrobat in order to use the product and that it you have PCs being access by users who do and don't have Acrobat licenses, then you need to install 32 bit version of Acrobat Pro and Adobe Reader in parallel.