I use cute PDF, it's free and doesn't leave any watermarks etc.
I've not done A1 size, but I've done A3.
I just did a quick test by creating a picture in MS Paint at those pixel sizes, then set page setup to ISO A0 then printed to PDF and is appeared to work ok
You can choose different paper sizes.
Possibly depends on other software and settings used to view images??
I went in a mine once.... it was dark and scary..... full of weirdos
When do I get my soapbox, I need to rant on about some b***cks