Currently, the built-in PDF viewer lacks a few key features, in addition to the already-reported missing find functionality (https://orionfeedback.org/d/278-cant-search-text-on-pdf-files)
The Firefox one:
And the overspill menu:
From a minimum viable perspective, I think main feature for me is page counter (to find a given page, or navigate to a page someone refers me to), the download button, and rotation buttons.
"Open with Preview" is good to have in the context menu, but I'd also suggest a right-click context menu option for "Download file as..."