A PDF is hard to edit, and many upload forms and image tools want pictures instead. HTML opens in any browser and can be published on the web as-is. PDF is at home in documents that must look the same everywhere, and printing; HTML is the usual choice for web pages and emails.
The defaults suit most files. Under Options you can choose which pages to convert and set or supply a password.
Only the text and its outline (headings, paragraphs, lists) are rebuilt. Tables, columns set side by side and images do not survive, and a scanned PDF, which holds pictures of pages rather than text, yields little or nothing because ToAny does not do OCR. A password-protected PDF needs its password, entered under Options; without it the file is refused.