I have 2 questions about 3D symbols in Creo Illustrate
1. How can I add a 3D symbol to Illustrate? Should this symbol be of the .ol file type? If yes, with what software can I create an .ol file?
2. Where are the sybol library files located? In the manual it is said that the path is \ users\<user_name\AppData\Roaming\PTC\Illustrate\SymbolsLibrary sha but on my laptop such a directory is not visible.
I can only answer question two: the folder they mean is a hidden folder.
For making it visible you should open the data-explorer.
Now it should work. Sorry for having the screenshot only in german. I cannot grant that the names are correctly translated.
For your first question, yes they need to be in .ol format.
See this previous question on the forum for a little more detail on how to create an .ol: