I've googled for this, without success. The few hits I got referred
to older versions of Irfanview, and the current options don't match
those screenshots.

I have 4.60, Irfanview 32-bit in Windows 10, with same version
plugins. In Properties » Plugins » PDF Options, I have "new plugin"
selected for both loading and saving.

Previously, after I saved an image as PDF, the PDF file would
automatically open (not in Irfanview, but in my default PDF viewer)
so I could check it visually and redo it if it wasn't formatted
right. With this version, the PDF still gets created but does _not_
open automatically, so I have to open Explorer, navigate to the file,
and double-click it.

While I would prefer to have the PDF open in my default viewer, as it
used to do, if I could get it to open in Irfanview that would be
better than nothing.

--
Stan Brown, Tehachapi, California, USA https://BrownMath.com/
Shikata ga nai...