JAR

JAR files are a format for distributing Java software. They are standard compressed ZIP archives with a .jar extension containing various further files including the Java classes themselves. These archives can be dissected and reassembled with any ZIP archiver. See the Wikipedia page on JAR files for more details.

PTViewer is generally supplied as a JAR archive. It is possible to create a custom ptviewer jar file that contains just the extensions you need and even a preview image.