The viewer stores its state data in local INI files. The storage folder used for this depends on the OS. The file name is based on the name of viewer executable. You can have custom eViewer deployments installed in the same folder. To enable this, the INI files are named as an MD5 hash of the executable.
Example of an state data file name:
eViewer107e80d67e78231fdbc518c8ff7d6723.ini
File contents:
•Owner (the application that created the file)
•Window position and maximized state
•Recently opened .ewriter files
Windows data storage location
C:\Users\<WINDOWSUSERNAME>\AppData\Local\com.ecsoftware.eviewer\
MacOS data storage location
/Users/<MACUSERNAME>/Library/Application Support/com.ecsoftware.eviewer/