TopLeaf is a 32-bit application which will install and run properly on 64-bit Windows systems.
However, you also need a 32-bit Java run-time in order for some functions, such as PDF creation, to work.
After installing 32-bit Java, select the run-time in TopLeaf's "Preferences" dialog, on the "Folders" tab.
You can find 32-bit Java run-times here:
http://www.oracle.com/technetwork/java/javase/downloads/jre7-downloads-1880261.html