You may need to update the version of Adobe Reader on your PC. Go to Adobe Reader
(http://get.adobe.com/reader/) and download the latest version. Once the install is complete, try
clicking on the file link again in ULearn and the document should open immediately
Other solutions:
1. You may save the file to file system. Right click at the PDF file link --> choose Save Link As.... Then try to open the file using Acrobat Reader.
2. Try to use different browser to open the PDF file.
The details is here: https://helpx.adobe.com/acrobat/kb/cant-view-pdf-web.html
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