Bedrock uses the same PNG format as Java. However, the file naming is different.
Action: Copy all .png files from the Java JAR into your new Bedrock resource pack's textures/ folder. Convert Jar To Mcaddon
This is where 90% of the work lies. The Java mod's functionality (e.g., "When I right-click this wand, explode fireballs") must be rewritten in Molang and Event-Driven JSON. Bedrock uses the same PNG format as Java
If you want a complex mod (like a new biome or vehicle mod) on Bedrock, you have to rebuild it. This is how most popular add-ons are made. Action: Copy all
.zip to .mcaddon."Convert Jar To Mcaddon" appears to describe a conversion or migration process between two package or module formats: a Java ARchive (JAR) and a format named "Mcaddon." Since "JAR" is a standard Java packaging format, this discourse treats the task as converting or adapting a Java-based artifact (code, resources, libraries) packaged as a JAR into the Mcaddon format used by a target platform that expects Mcaddon packages.
If you meant something else (a file-naming convention, a specific tool, or a game mod format), the steps below still apply as a general guide for migrating from a generic Java JAR to a different package format.