Where PDF came from
Adobe created PDF in 1993 to solve one problem: a document that looks identical on every screen and every printer. It became an open ISO standard in 2008 and is now the default format for anything that functions as a record — contracts, invoices, forms, submissions, archives. Its fixed layout is precisely why bureaucratic systems prefer it to a bare image attachment.
The technical picture
Compression: Container — embedded images keep their own encoding. Transparency: Supported, though most viewers composite onto white. Animation: Not applicable. Colour: Device-independent, ICC-managed. Typical file size relative to WebP: roughly the size of the images it wraps, plus document overhead.
Where it opens
Universal — every OS ships a reader. This is usually the deciding factor when choosing between PDF and WebP — WebP renders in every browser but is uneven in desktop software, while PDF has a very different support profile.
Converting PDF to WebP
Rendering PDF pages to WebP gives you compact page images you can put straight into a web page, a docs site or a preview thumbnail strip — typically half the weight of the equivalent JPG render. A page image is no longer a document: text cannot be selected, searched or copied. Keep the source PDF for anything that needs to stay readable by machines.
Converting WebP to PDF
Almost every formal destination — application portals, expense tools, insurance claims, government forms, print shops — wants a PDF and will reject a raw image, let alone a .webp. Wrapping the image in a properly sized A4 or Letter page turns it into a document those systems accept. Expect the PDF output to be roughly the size of the images it wraps, plus document overhead — that difference is the price of getting a format the destination will actually accept.