I am sorry to say, that the instruction-notes in the received package do NOT work!
Please let me know what instructions you are referring to and I will try to help further.
What VISIBLE differences are there compared to the free version of Autoviewer?
In swapping over the Standard SWF file for the Pro SWF file provided in the AutoViewer Pro download package, the only visible difference is that the AutoViewer badge/link is no longer visible in the bottom right-hand corner of the gallery.
AutoViewer Pro gives you access to the Pro Options which are not available to AutoViewer Standard users. If you were to publish and use your own customized Pro SWF file (incorporating some of the Pro Options), then you may see many other visible differences (depending on the Pro Options used).
Or: do I need an expensive piece of software like Flash to get the full benefits of Autoviewer Pro?
As noted on AutoViewer Pro's main page:
Customizing AutoViewer-Pro requires Adobe Flash 8 (or later) authoring software. A free, fully functioning 30-day trial of Flash can be downloaded here. AutoViewer-Pro is written in ActionScript 2. To just remove the download link from AutoViewer, it is not necessary to use Flash. View instructions.
You can use the free trial of Flash to create several different SWF files, each with different Pro Options for future use.
SimpleViewer Support Team