I remember Okular having a decent set of features. It might be worth checking out. The webpage says it supports digital signing, which is a suprise to me because that’s always been a hassle on linux for me. https://okular.kde.org/

I haven’t tried a USB adapter with proxmox, but there’s a chance it would work. I was also looking at a cheap pcie card like this one as a way to add another ethernet port. https://pcpartpicker.com/product/dQmLrH/tp-link-wired-network-card-tg3468

That being said, the steps in the link that David gave have worked for me to stop the hardware hang issue with the intel nic. Basically disable tcp segmentation offload and generic segmentation offload with ethtool -K eno1 tso off gso off. You can add a post-up command to the interace config to make it persistent.

I had the same thing with the intel nic having hardware hang issues. Definetely recommend mitexleo check out that link. If it is the same thing, you can unplug and replug the ethernet cable to at least get communication to the host again without restarting the computer.