Uploading files must be done one at a time within each target folder; there is no bulk upload feature to add documents to multiple locations simultaneously. When you upload a file in the organisation-wide Documents library, you can optionally assign it to a specific Location folder by choosing a Site, but this is always done per file and folder. Similarly, when uploading from a Location’s own Documents tab, the file is automatically filed under that Location only.
Documents are managed within the Documents library, where you can create folders that inherit Location access. Only users with report-create permission (typically Engineers or higher) can upload files; Viewers do not see the upload option. Owner-level folders at the organisation level can be added to only by those with appropriate permissions for that level.