tried to add
system.openoffice.path with the value .. C:\tomcat-8.5.24\extras\LibreOfficePortable\App\libreoffice\program
i can see the previewer but it would just display on the page
"There was a problem with the conversion generation.
Please, contact your OpenKM administrator."
Update: I think this is the problem.
2018-08-30 14:41:15,128 [localhost-startStop-1] [] WARN c.o.servlet.RepositoryStartupServlet - invalid officeHome: it doesn't contain soffice.bin: C:\tomcat-8.5.24\extras\LibreOfficePortable\App\libreoffice\program
java.lang.IllegalStateException: invalid officeHome: it doesn't contain soffice.bin: C:\tomcat-8.5.24\extras\LibreOfficePortable\App\libreoffice\program
but this path has soffice.bin