Pull the text out of a PDF as tidy Markdown - here in this tab, with nothing uploaded.
The PDFs people want as Markdown are usually contracts, papers and reports - exactly the documents you should not hand to a converter you know nothing about. This reads the PDF with the same engine your browser uses to display one, here in the tab, and sends nothing.
By size. The most common font size in the document is taken as body text, and lines set noticeably larger become headings, with the largest as level one.
It is almost certainly a scan: pictures of pages rather than text. Getting text out of those needs OCR, which this tool does not do.
Their text is, row by row, but PDFs do not record tables as tables - only as text placed in columns - so complex tables usually need tidying by hand.
Not while they are locked. Remove the password first, then drop it in.