Persisted data is stored in SumatraPDF-settings.txt file.
In portable version the file is stored in the same directory as SumatraPDF executable. In non-portable version, it's in %LOCALAPPDATA%\SumatraPDF directory.
Starting with version 1.6 we also persist thumbnails for "Frequently read" list. They are stored in subdirectory sumatrapdfcache as .png files.
See https://www.sumatrapdfreader.org/settings/settings.html for information about all the settings.
To add more settings:

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