Free, but not sure about open source... LibreOffice Draw works well. Inkscape is worth checking out; typically a vector graphics tool, but also has some PDF editing capabilities.
I've used Foxit PhantomPDF across a few clients, and have had some issues with the driver just randomly experiencing issues when trying to print to PDF or to a printer. So, just a heads up. But their price is very attractive. As @JaredBusch also pointed out, PDf Element is a good alternative at a slightly lower cost than Foxit PhantomPDF (roughly $30).