With Kotlin as Java plugin applied, all Kotlin signatures will be rendered as Java signatures.
For instance, fun foo(bar: Bar): Baz will be rendered as public final Baz foo(Bar bar).
The Kotlin as Java plugin is published to maven central as a separate artifact:
org.jetbrains.dokka:kotlin-as-java-plugin:2.0.0
This plugin is at its early stages, so you may experience issues and encounter bugs. Feel free to report any errors you see.