I recently downloaded the Pattern Tool because I wanted to poke around its files a little bit, but it seems that the fullbuild.package for the tool is an "ENCR asset pack" as opposed to a DBPF package and S3PE can't open it. Do we know how to decode these archives?

ENCR asset pack is a new term for me, do you happen to have a link maybe, or could you elaborate a little on that?

Not sure if this tutorial will help, but indeed some pattern tool created packages have a different header bit, so this is a way to convert them: https://simlicious.tumblr.com/post/...ted-patterns-in

Thanks for the link, but it seems like this file is something different entirely. I did manage to extract some of the contents with a HEX editor, as luckily it seems like (some of) the files aren't actually compressed, but I only tried it with some sound files. Here is a link to the file if you'd like to take a look.

I haven't been able to make much sense of the file header, just some mysterious bytes and then the actual file contents.
I also had a bit of trouble actually downloading the tool, the download button on the official page doesn't seem to work anymore so I'll leave this direct link to bypass it.
https://www.thesims3.com/content/gl...3CAP_767618.exe