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.
To add more settings: