Can't open pdf's

Can't open pdf's

Hello to all
I have recently changed from macOS to Linux Mint. I could also download the Zoho Notebook, which I greatly appreciate, and my notes were there as expected.
Not only that, but I can not open all the many notes saved in pdf, which is off course not really good

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        Zoho Notebook is transforming. The new version will include exciting new features and a completely new user experience. The initial version will be mobile based, available for Android and iOS. A new web version will be available after the initial mobile release.   With the release of the new Notebook approaching, we're migrating most of your current data to the new version. Once the new version is released, there will be an additional window to migrate your data. We will not provide access to the