Have you considered keeping (or tweaking) your current folder system and putting it in an Obsidian vault?
The advantages are that you’d still be able to keep your pdfs as they but also tag and link them. (And if you doing like Obsidian you keep your files untouched.) Obsidian has lots of plugins that would help. Plus the Obsidian community has lots of TTRPG-ers who do some amazing things in Obsidian. And it’s all free.