Get something else out of a PDF

Glyphs at coordinates. A PDF records that a particular character from a particular font was drawn at a particular position, and nothing about what that character was for. There is no heading in the file, no list, no table and no paragraph — those are things a reader infers from size, weight, indentation and alignment, and it is what these converters infer too. The signals are strong and usually right; check headings and tables before you rely on them, which is why the Markdown tool shows you its output before it offers a file.

Take Word when somebody has to edit the text: you get real Word heading styles, real lists, tables where the columns genuinely line up, and bold and italic within a line. Take Markdown when the text is going into a notes app, a repository or another tool. Take images when the appearance is the point — a page as a picture is the only conversion that keeps the layout exactly, and it is the one that gives up the text.

A scanned page holds a picture of text and no characters at all, so there is nothing for a converter to extract and no way to recover a character that was never in the file. Reading letters out of an image is optical character recognition, which these tools do not perform. Rather than hand you an empty document that looks like its own bug, the tool names the pages that have no text layer and produces no file.