Game Manuals
This one is pretty self explanatory - having a dedicated image category to reserve for game manuals. While it would be incredible to have a method of flipping through the images like a book, just attaching a PDF would still certainly be better than nothing. It's a definitely overlooked but essential piece of preserving game information, and it would be great to have it here.
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shashadmo commented
One of the major advantages of PDF documents is their security. Sometimes features like locking a PDF file with a password come in handy. Although it's not always convenient (I've forgotten the password a couple of times), I use this tool https://www.pdfplatform.com/unlock to quickly remove the password without compromising data security.