From personal experience browsing websites, especially sites that display catalogues, manuals, or specifications, a whole lot of them produce PDF content and then go out of their way to render it with JavaScript. The worst use horribly performing systems that make consuming the content miserable. Better commercial systems are a step up (Issuu is a whole company that seems to be developed around doing this). Even better ones use PDF.js. But the best ones... drumroll please... just link to the PDF as Content-Disposition: inline. If users want to save it, then they click save. And this is great -- you want your users to have the easiest time possible interacting with your marketing material.
> fill forms in the browser (where their authenticated context resides)
I have never, in my entire life, seen a web form implemented as a PDF where this was anything other than miserable. Use a form, thank you very much. The less SPA magic and the fewer intermediate submit buttons, the better. (Maybe, if the actual goal is for a user to fill out a form and print the result, offer PDF.js to users on Windows who might otherwise be stuck with Acrobat. I distinctly remember Acrobat being the best PDF-form-filling software maybe 20 years ago, but Acrobat has gotten, if anything, worse, and basically every other package out there runs circles around it.)
> fill forms in the browser (where their authenticated context resides)
I have never, in my entire life, seen a web form implemented as a PDF where this was anything other than miserable. Use a form, thank you very much. The less SPA magic and the fewer intermediate submit buttons, the better. (Maybe, if the actual goal is for a user to fill out a form and print the result, offer PDF.js to users on Windows who might otherwise be stuck with Acrobat. I distinctly remember Acrobat being the best PDF-form-filling software maybe 20 years ago, but Acrobat has gotten, if anything, worse, and basically every other package out there runs circles around it.)