Download JD-GUI to open JAR file and explore Java source code file (.class .java)
Click menu "File → Open File..." or just drag-and-drop the JAR file in the JD-GUI window daml-lf-1.16-archive-proto-2.9.0-snapshot.20240418.12747.0.v0bbede5e.jar file.
Once you open a JAR file, all the java classes in the JAR file will be displayed.