Are bookmarks, links, forms and metadata kept?
Yes, as long as a file keeps all its pages in their original order: its pages are changed in place rather than copied into a new document, so bookmarks, internal links, annotations, editable form fields and document metadata remain. If you also move or delete pages, or combine files into one PDF, pages are copied instead and the Save panel says so before you save. This is not a metadata-removal, sanitization or redaction tool. Review the result before distributing it.