Is there any specific reasons you cannot import the external JARs to the PegaRULES database?

The preferred mechanism to add a custom jar to Pega 7 is to load the jar into the database. However, we do realize that some users prefer to add these to the file system within the WAR or EAR file.

While discouraged, this does work but requires a couple of additional steps beyond what was required in the 6.x releases. We have explicitly not documented this process in the installation manuals or on the PDN in order to avoid any possibility of "encouraging" users to follow this approach. However, for special requirement / cases PegaSupport can help with the detail instructions.