My problem is I can't get Qimage to print to a PDF, why is this feature blocked?
Nothing is blocked! QU does not have a built-in print to pdf feature like Microsoft Word.
You need a separate PDF "Printer" such as Tracker software PDF-XChange V6 Printer Driver. You can download the free version here
https://www.tracker-software.com/product/pdf-xchange-lite.
This appears as a printer in Devices & Printers so will show as a printer in the QU list. See the screen shot below.
Also you will see the Microsoft pdf printer (I'd forgotten that!) but the Tracker driver is much better.
Re.
I would like to send the output of Qimage to a PDF file and have that file spooled at the printer on the Linux system next to it. When ready for the next job the Linux system send the spooled PDF to the printer, pretty basic stuff
For images, you'll have to be careful with the printer profile used for the pdf printer, I don't believe pdf files are colour managed. I set sRGB and got reasonable results.
It's not the way to reproduce best quality images.
Terry