Put any person who has zero computer experience in front of a windows computer or Linux computer and I doubt they would say the windows computer just works and the Linux one doesn't.
In my experience, usually with Linux they have less problems and it's easier to use. Until they need an application that only works on Windows.
On the PDF to JPEG, you can also open the PDFs with an image editor, such as Inkscape or krita, and then save the image on the format and quality needed. This method also has the benefit that on some cases you play with the assets if needed. (Depends on how was the PDF generated)
Usually what i do is look for any converter and look for open source alternatives to it on alternativeto.net and hopefully one of the top 3 alternatives fits your use case
It seems like something that could be improved by 3d printing.
I'm guessing that if a vet has to assist several animals of the same species maybe it could be possible to get some kind of mask that could fit most of them.
Although I'm not sure if that's something that would help or maybe it will just be more cumbersome.
There you can check pricing of several registrars for your domain and choose the one that you want and then you can see how to transfer to the chosen one.
In my experience, usually with Linux they have less problems and it's easier to use. Until they need an application that only works on Windows.