Intellij IDEA - How to disable automatic plugin update

The best way would probably be to not install it from the plugin repository. Try to install it from disk instead. Download it from the link you provided instead (the zip file will be downloaded):

Then choose to Install plugin from disk... instead:

And then point to the pmd.zip file:

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Edit

During the update you will get a question whether you want to update the plugins as well and you can always uncheck that plugin:

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Edit2

Make sure that you don't have the Check for updates in channel checked. That might help you out: