I just checked on my Win 10.
javadoc is not part of the jre folder. (Java runtime environment)
https://www.oracle.com/technetwork/java/javase/documentation/javadoc-137458.html
It’s only part of the Java 2 SDK. This contains JRE and compiler and debugger (160 MB I think)
https://www.oracle.com/technetwork/java/javase/install-140406.html
PATH
also when you have javadoc, make sure windows knows the path of it:
(example from another program)
https://docs.telerik.com/teststudio/features/test-runners/add-path-environment-variables