What page? Advanced Item Categories? It's a custom variant by Gurnikan on the BGG forums, the manual and cardbacks were made by zee Parks for this variant so people could print both out and have an official look to it(so not officially published).

Where the hell is this page from?

Ok new update changes it to the Steam Cloud(originally didn't use Steam cloud as it wouldn't upload, which seems to have been a problem with the PDF file). Originally chose gdrive as it was the only option that'd work that allowed images over 20mb in size(dropbox just wouldn't work as I couldn't get a direct link to the actual images that TTS would accept).

Hopefully it'll work better with the cloud!

This is always such a pain in the ass to explain, but here it goes.

Tabletop Simulator caches what it downloads onto your disk so it can doesn't need to download the same data again later. The filenames are equivalent to the URLs with all the punctuation stripped out, with the proper extension added. For instance, https://i.imgur.com/N0O6aqj.jpg becomes httpsiimgurcomN0O6aqjjpg.jpg on the disk.

Unfortunately, Windows has a limit to how long a filename can be. This makes GDrive a very poor choice of host, because the URLs you're working with are like this:

https://lh3.googleusercontent.com/WkB1Ea4ZnWZMBf6hTVC8A_DLcZux7v_xyC2A56CnRF7P0n3A8r4IBm14htsDos7Cas5XJYpghhEy6fMgvQlEy60c-oToczF5E_87SuFWoIPzbAZAL4Eo24n948gxYo6DneySyqo0l8H23JAjJQW-o7C0dOv8Er0uhkqLmOjwWPWocGSbDG1ymuycRR6m1kK6FnEWr-EesYErJ4YXFNtcZvUPpFXSyzEkEpefxiQh9AxlBHkdwnG8iGMWSmEk24_iQCozSoX6jpScUQJ_8R7UzntnrovK8the3lt6NiHlHV4u_Jq4D_ndvxLnCXPMNfDsW8MWAbAEDtMyCYjwYTRO9V7dkiBcqOQnaNbp5ESEwRmrtkQNYTLKyJVC5Ig-lfwaKPpoFjTWpb0fg2RF3IPzywfzG_Sb9htOU3VOTe9Pb8tlWVI_soED6quQ_vjcaeMuIRorJNlDY0meqAAvGQ_THZHOc6dkrU4JoNBKiGQhljSaBgN7MmaHGtrXw2Np2qY3sVLQ819hyFhAqbx_6Bs2aYPmlDQrOTZMeQyMgEjiDb3l1ztuaaLuSX1UlwdPeJahjqDThA4wLJ9f3dV-LU-OUPJMuLhp2RY-gxOfw8uXDniasGsYyCbNMoO6St2FBhS7SRYHCvJ3PHj_QMsm3jO8dneH3nsc74tJPP39jnABebp4Qb7O3ZFe3Q=w1740-h805-no

which becomes...

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.png