PageFabric requires some read and write access to your PC to work properly.
By default, application have write access to the current user profile ("%userprofile%\AppData\Local").
Your application settings will be stored in "%userprofile%\AppData\Local\PageFabric".
When your launch the application for the first time, a new folder called "PageFabric Websites" will be created in the Documents Library.
In the latest versions of Windows 10, a new security feature can totally block access to this folder. When this feature is enabled, PageFabric cannot access to the Documents Library. This will prevent the application from working correctly.
Feature description on Microsoft: https://docs.microsoft.com/en-us/microsoft-365/security/defender-endpoint/enable-controlled-folders?view=o365-worldwide
Read this article to allow applications and folder: https://support.microsoft.com/en-us/windows/allow-an-app-to-access-controlled-folders-b5b6627a-b008-2ca2-7931-7e51e912b034