Choose a source format. JPG to PDF, PNG to PDF, and the other converters each accept only that image type.
These pages stack images into a PDF in your browser. Order matters (ID front then back). Transparency in PNG flattens onto the page background. Compress the PDF if email still rejects the file.
Civil ID PDF Maker is the better template for a two-sided card layout. JPEG-spelling URLs stay linked as helpers for software that only accepts .jpeg.