In the context of OSS bucket, the files can only be deleted by API call DELETE buckets/
If in the context of SaaS cloud products of Autodesk, the files can be deleted by end user or by API (another blog tells more). However, there is something difference between BIM 360 Docs projects and the projects of other types cloud products such as Fusion Team, A360 etc.
In the project of BIM 360 Docs, the property (attributes>>hidden) will be true after the items (file or folder) were deleted from BIM 360 Docs projects. They are NOT permanently deleted and remain hidden until they are restored. When you call GET projects/:project_id/folders/:folder_id/contents, it returns files that are not hidden. By the filter 'includeHidden=true', or 'filter[hidden]=true', it will return the files that are hidden. However, items and folders that are deleted from other types of projects are immediately permanently deleted and cannot be hidden. Before they are deleted they are tagged as hidden:false.
This blog is rather a repeating of API help: https://developer.autodesk.com/en/docs/data/v2/overview/filtering/. check this link for more.