Where all these .webp files came from
WebP is a Google format from 2010 that took a decade to matter. It compresses about 25 to 35 percent smaller than JPEG at the same visual quality, so once every browser supported it, every large site switched. Your browser advertises WebP support in its request headers, the server sees that and sends WebP, and the file you save is WebP.
Which is fine, until you try to put it in a document, attach it to an insurance claim, or open it in a piece of software that stopped being updated in 2018. Then you need something else, and PDF is the something else that never gets rejected.
WebP against the alternatives
| WebP | JPEG | PNG | |
|---|---|---|---|
| Lossy compression | Yes | Yes | No |
| Lossless mode | Yes | No | Yes |
| Transparency | Yes | No | Yes |
| Animation | Yes | No | No |
| Goes into a PDF unchanged | No | Yes | No |
| Accepted by upload forms | Often not | Always | Usually |
That fifth row is the whole reason this page has to re-encode. A PDF knows how to display a JPEG stream directly. It has no idea what WebP is, and it never will, because the PDF image filters were frozen long before WebP existed.
Stopping your browser saving WebP
On desktop Chrome and Edge there is no setting for it, which is the honest answer. What does work: open the image in its own tab first, then save it, because some sites serve the original JPEG at the direct URL. Failing that, a screenshot of the image is a PNG, which is lossless from the pixels on your screen and often good enough.
Firefox behaves the same way. Safari on macOS often saves the original format rather than the served one, so if you have a Mac, that is the shortcut.
Animated WebP
An animated WebP is a container full of frames, like a GIF. This tool takes the first frame and puts that on the page. There is no version of a PDF page that plays an animation, so any tool claiming otherwise is either extracting one frame like this one or embedding something your PDF reader will refuse to run.