Open your steam library, right-click Garry's Mod, go to Properties > Local Files > Browse Local Files
Next go to garrysmod > data.
Here you will find all folders related to PAC, look below for more information.
All paths below are relative to the data folder so /pac3 is <gmod_folder>/garrysmod/data/pac3
| /pac3 | The main PAC folder, all you outfits are kept in here. |
| /pac3_cache | The cache folders, it contains cached models and .zip downloads. Deleting this folder will clear the cache. |
| /pac3/__animations | Custom animations folder, contains all the saved animations. |
| /pac3/__backup | Backup folder, contains backups automatically created by the editor. |
| /pac3/__backup_save | Save backup folder, contains backups created while overwriting saved outfits. |
Keep in mind this only covers the latest version, your folder structure might be a bit different if you're using an older version.