The content blocked error is likely due to Adobe and/or internet browser setting.
Adobe has provided the following guidance that explains which browsers may not support opening PDF documents and how to troubleshoot: https://helpx.adobe.com/acrobat/using/display-pdf-in-browser.html and https://helpx.adobe.com/acrobat/kb/change-in-support-for-acrobat-and-reader-plug-ins-in-modern-web-.html
Make sure they are using a desktop computer on a compatible browser like Google Chrome (not a tablet/phone or Safari). Also try multiple browsers including Google Chrome and Microsoft Edge.