PDF to JPG saves the pages you choose as pictures, one at a time or all together in a ZIP file, at the level of detail you need. JPG to PDF takes JPG and PNG pictures, puts them in your order and turns sideways photos the right way up, one picture per page. Grayscale PDF redraws every page in grey, for printers and for submission rules that ask for black and white.
You can convert PDF and images free, with no sign-up and no watermark, as often as you like. Everything is converted inside your browser, so your photos and documents never leave your device.
What it does not do: it does not read the words in a picture (that is OCR), and it does not convert to or from Word. The text in pictures made from a PDF can no longer be selected.