How do I process the RTF data in a paste buffer?

PS in an AS/JXA script, the theClipboard method of standard additions should, of course, also yield any textual version of the available pasteBoard contents:

Applescript

use scripting additions

the clipboard

JavaScript for Automation

(() => {
    // standardAdditions :: () -> Library Object
    const standardAdditions = () =>
        Object.assign(
            Application.currentApplication(), {
                includeStandardAdditions: true
            }
        );

    return standardAdditions().theClipboard();
})();