Other packages probably don't create useful output. I doubt you'll find a PostScript plugin for Altium (printer output sure, but that's full page, what if you don't want the full page?), or most any others. PDF is fine, but you have to crop it down to embed a schematic rather than a whole sheet.
In the past, I've used 125 or 300 DPI bitmaps, which aren't bad considering. Also "free" software used to create them (Paint!).
Tim