Add PDFs and images, put them in order, and merge them into one PDF. Each image becomes its own page. Everything happens in your browser; nothing is uploaded anywhere.
Tip: drag the ⋮⋮ handle or use the arrows to reorder. "Make every page A4" shrinks or enlarges each page to fit, so a big scan and a normal page come out the same size. Password-protected PDFs can't be merged. iPhone HEIC photos aren't supported; export them as JPG first.