How to create a pdf picture

Your question is not entirely clear, do you want to convert a vector pdf to a raster pdf, or do you want to convert an image format (jpeg, tiff, etc.) to a pdf?

You can use a preflight fixup to convert pdf content to raster, Tools> Print production> Preflight> Fixups. To convert an image file to pdf, open it in Acrobat and save as a pdf.

Design it in your favourite app, then make a PDF from it. Don't look for a PDF editor.

In Acrobat via File - Create...