Chrome has its own Integrated PDF Viwer, when I click on links to online PDFs, they are opened by it. Just hovering over the bottom right corner of an opened PDF, pops a little toolbar with options to zoom, print, save, etc.
But to open local PDFs, what I do is manually edit my mime types so PDFs are opened by Chrome. I use Xfce and it has a nice mime editor. But by just right clicking a PDF file on the file manager and choosing the
Open with option, then selecting Chrome from the list and making sure the Always use this application for this kind of files is checked, I get the same results.
I'm sure KDE works in a similar fashion.
Finally you didn't want extensions mentioned but this one, opens not just PDFs, but a plethora of other formats online, using Google docs viewers. It also opens online PDFs (In mi case, I have it not open PDFs, only some other formats)