Yes — it reads the real ZIP/OOXML structure directly, including DEFLATE-compressed files (which is how Word actually saves .docx files), via a hand-built ZIP reader.
Paragraphs, heading styles (Heading1-6), and bold/italic/underline text runs. Tables, images, lists, and embedded objects are not converted.
Yes — upload multiple files and each is converted independently, with a combined "Download All (.zip)" option.