The issue could be that the ebook PDF is trying to open in the web browser’s default viewer rather than in Adobe Reader. You could try adjusting the default settings in your web browser to use Adobe Reader or Adobe Digital Editions instead.
If you are using Firefox check your settings by selecting Tools > Options > Applications and then make sure that Adobe Reader or Adobe Digital Reader is selected to open PDFs.
If using Chrome you can check your setting by selecting Settings > Advanced > Content Settings in the Privacy and Security section. You can experiment with switching the PDF statement “Download PDF files instead of automatically opening them in Chrome” on or off and see if this helps.
If using Safari you can set the browser Preference to use the Adobe Reader plugin. In the Preferences window select Security and then click ‘Website Settings’ for Internet plugins. Now select Adobe Reader from the list. Under the option ‘When visiting other websites’ choose ‘Allow Always’ in the drop-down list and click Done.
Further details on enabling or disabling web browser and Adobe settings if you experience issues opening PDFs can be accessed from this Adobe help page.
