Checks the compression of the PDF structure (possible as of PDF 1.5).
You can also check if the compression is compliant with PDF/X.
In a PDF, objects have content streams that define (a part of) the object. These content streams can be compressed in order to create smaller files, so this is mostly used if a PDF is to be put on a website. As older RIPS may have problems with this compression, this Action allows you to check if the PDF contains such compressed streams, which you can afterwards remove if required.