The "Pay what you think it’s worth" page is for statistical analysis on what you think is worth most in terms of further Ubuntu development only. It will by no means configure your Ubuntu or even change anything on the applications that are installed for free. The page you see asks for a voluntary donation, not more not less. You still can download Ubuntu for free.
Ubuntu and most of the software included are Free and Open Source Software which means they are really free in terms of monetary costs but also are free in terms of usage.
Read more on this here:
As for applications to process graphics and multimedia the same holds true. The most useful applications will be included for free with every Ubuntu distribution. Below applications - to name only a few - are only a mouse click (and some internet bandwith) away once you had installed Ubuntu:
- Gimp - A powerful graphics processor highly extendable with plugins. Comes close to Photoshop in functionality.
- Inkscape - full blown vector graphics application similar to Illustrator.
- Blender - a 3D modeller which can produce professional results.
- ImageMagick - unbeaten versatile command line tool for almost all graphics file manipulation and conversion.
- Audacity - a great sound processor.
- OpenShot - easy to use video editing software but with somewhat limited professional capabilities.
- Cinelerra - not in the official repositories due to stability issues but once running stable it is an ambitious video editor.
- and there are many many more.
But if you are seeking paid software with widespread use by professionals, paid support, paid courses and paid tutorials you may be wrong here. This is where the products on Microsoft and Apple platforms still are better.
You also may find it hard to switch to an Ubuntu application after you had learned how to do things with the software you mentioned. This also would be a good reason to stay with the system you already have.
Last not least we still occasionally have issues with import from or export to proprietary file formats of paid software. This is being resolved step by step but we will never beat the originals.
So you should try out these Open Source softwares which often are available on your Windows or MacOS too. If you find them useful, and if you do not miss anything from your proprietary paid software then you are safe to make the switch. But if you expect all softwares to work identical to their paid counterparts you should propably better stay with Windows or MacOS.
Few professional Windows software may run flawlessly on Ubuntu but this is not the case for most. Software made for Apple computers will not run on Ubuntu.