Are you adding the files as hyperlinks or attachments?
Also which browser are you using? If chrome, can you try mozilla or IE.
If you are trying to open the PDFs when testing by playing the content from your local C drive, you are likely encountering Flash Security Settings blocking the links.
Take a look at the link below for more:
I'm adding them as attachments. I'm uploading them to the LMS so not viewing them locally and using Internet Explorer 9. What's so odd is that only some of the PDFs open.
The PDFs open on their own - outside of any course.
I don't know what else to troubleshoot.
I am not able to understand when you are saying that a few pdf's open and others do not.
It would be good if you can mail the presentation package so that I can look into your issue
Please mail it to firstname.lastname@example.org. If the package is very huge please upload it to acrobat.com
I will try to look into your issue