Editors such as Overleaf, and those offered by MS and Adobe, have been around for a long time. Recently, companies like Pandadoc and Docusign have started offering services around PDFs (generation or other aspects of their lifecycle).

It might seem odd, given our long history with PDFs, but I believe there's still much to be done with these documents. They're everywhere—invoices, tickets, reports, etc.—yet the technology for generating and managing them hasn't evolved much in years. Our approach is to apply the same modern technologies used for web design to document design.

What do you mean "now"? It has been for years. It's a huge business.

When I was first hired 15 years ago my first task was to create a PDF report. It was easy back then in PHP+fPDF. Two years ago I was hired to work on a Heroku-hosted NodeJS app. I was surprised to find that generating a PDF turned out to be substantially more difficult task, requiring running a browser emulator or connecting to an external service. And now, seeing PDF generation as a premium pay-as-you-go product is just too much.

Makes sense. Actually, if you keep the layout/content very simple, aren't constrained by throughput, and don't need to integrate dynamic data or other similar processes, then simple FOSS could indeed get the job done! That's exactly why we developed the open-source library react-print-pdf

There have long been free HTML-PDF options around, but at the same time commercial products that offered more features. Some examples are opening an existing PDF and modifying it, adding to it, merging PDFs, or filling PDF forms.

I'd literally spin up a PHP container with TCPDF and do caveman math on cell sizes. Making something fancy with it is a lot of work, but it is a steady, incremental work. Doing stuff with HTML+CSS conversion is just frustrating and you'll likely get 90% there then spend most of the time kicking and bashing CSS until it behaves nicely in that obscure case. In TCPDF I was able to make a temporary page, write to it, check the positions, discard that page and arrange the actual content based on that. You can't do that with CSS, good luck guessing how much horizontal space the text takes