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I've sent out an update to The Keep v2 on the 'beta' update channel. This update changes how PDF files are viewed within the program. Rather than requiring the Adobe PDF viewer to be installed, The Keep now features its own PDF viewer (based on the one used in Chrome). The latest Adobe viewer was causing a number of people to see access violations when PDFs were viewed within The Keep, and/or when The Keep closed after a PDF was viewed. This update fixes the problem.
The integrated viewer is also faster. And by having an integrated viewer, PDFs can now be included when printing multiple topics (there's a couple new settings in the print window).
There's an 'open in viewer' option if you still need to load the PDF within the Adobe Viewer or other preferred viewer.
To get the update, switch to the 'beta' update channel (in Program Preferences, on the Updates tab), and then check for updates.
Let me know if you encounter any problems.