compress pdf from 300 mB to 10 MB

Lots of ways to do this, but first, is this a single page layout in X3? What resolution does your pdf file need to be at? What's the size of the layout? Letter? Custom?

If its just a single page layout, and you don't need much more than 150dpi for the pdf, and you don't need to edit anything within the file itself, you could just select all, convert to a bitmap at whatever resolution you want, then FILE>Publish To PDF. Once there, select your settings button and play around with the object parameters to get your filesize down small enough to your liking.

Corel doesn't always create the smallest pdf files either, so you may want to use something like Bullzip PDF Printer and just "print" your pdf files directly from your machine (assuming you're on a windows platform).

There are also settings from within Adobe Acrobat (full versions, not reader!) which can tweak your existing pdf files too, but I can't remember the exact spot for the settings, and I don't have it installed on my system any more.