PPTX: Document Properties are not exposed

Created by: Anonymous

Original issue 447 created by @ysavourel on 2015-03-02T22:19:17.000Z:

Reported by a user. Try extracting content from the attached file, with "Translate Document Properties" enabled. The document properties will not be produced.

This option works correctly for DOCX, but does not seem to work for PPTX.