How a .docx becomes a PDF here
The tool converts your document to HTML, draws it in your browser at A4 width, and slices the picture into A4 pages inside a PDF.
There are no options: you upload a file and click Convert to PDF. Headings, paragraphs, lists, bold and italic and similar basic formatting are converted. Because the pages are rendered as images, the PDF looks like a picture of the document, not a text-based export from Word.