As I wrote above, I build a bunch of converters. If PNG to PDF has no use for you, then maybe heic to jpg, or tiff to png, or webp to jpg? If you already have a quick and good solution for all of these (or you never need to convert in any of those ways), then that's fine too.

One example is that students often have to turn in files in PDF format but may not have a scanner for handwritten papers. It's not amazing quality, but this let's you take a photo with your phone and convert it to PDF for submission.

There are bespoke tools for scanning documents with your phone and exporting to PDF. The quality is MUCH better this way, as it automatically crops, aligns, and dewarps the image, plus applies filters to adjust the colours. You would have a hard time differentiating this from a proper scan.

(For example, Microsoft Lens: https://apps.apple.com/ca/app/microsoft-lens-pdf-scanner/id9...)

That's true. But in the situation with my accountant that led to me developing this, I already had a bunch of files on my computer. Some were screenshots of emails, some were photos, so this was a handy way to combine them all.

So you can make things like this: https://i.imgur.com/uq4a4PY.png

So... did you do PNG to PDF to PNG for that? :)