To switch to the Options window tap its button on the Control Panel:

or select menu item File | Options...

Display

Text size:
Sets font size.
Language:
Sets national character set. Automatic means that the program tries to detect charset from CHM internal data. Many CHM compilers ignore national charset settings while compilation process, in such cases you may want to set Language directly. This setting is remembered by CHM eBook Reader for each CHM file you read, not globally.
ClearType
Sets if the Microsoft ClearType technology is used for better font display.
Fit to window
Fits the current page to window size if possible.
Show images
Set display or not to display images.
Disable CSS
Turns CSS (cascade style sheets) ON/OFF. May be useful if you need to read text only.

Execute Script
- If this option is off, CHM file opening is much faster, but external JS files will not be
processed. JS files aren't used in most of CHM eBooks.
Show message "Merged file open error"
If you are reding merged CHM files, and one of these files is absent, "Merged file open error"
error occurs. Message abiut this error may be turned off.
Bookmarks

Autosave bookmark when file close
On file closing a bookmark pointing to the current place of the current page will be created.
Delete previous autosaved bookmarks
Autobookmarks set in last CHM view will be deleted.
Load last saved bookmark when file open
When file is opened, it will be displayed from the point stored in the last created bookmark.
Search

Highlight found words
All words found by Search function on the current page will be highlighted.
Scroll to first found word's position
Scroll to the first found word automatically.
Show 'Location' in search results:
Shows the name of the CHM file, in which this topic is located. Makes sense only if you're reading merged CHM files.
Menu

Max. number of files to show
Sets the Recent Files list length.
Show *.chm files names
Show CHM files name in the Recent Files list rather than their titles....
with full paths
...including their full paths on the Pocket PC file system.
Show books titles
Show CHM files titles.
General
Associate *.chm file extension with microOLAP CHM eBook Reader
Launch CHM eBook Reader on a CHM file tap, if this option is set.
Load last CHM file while program start
On program start last file from the Recent Files list will be opened.
Show program icon on the task bar
Sets if the program icon is displayed on the system task bar.