I take whole page screenshots regularly for documenting resource pages.
I use https://gofullpage.com/
It's free and does PDFs and PNGs.
I normally use PNGs since PDFs break up web pages at awkward spots.
I did check this extension out, it has Box like collaboration features. Blackboard is intended for personal use, eg- Save important web snippets with personal explanations (and organise in folders within a library - coming soon. So yeah good features will be combined slowly in future releases!)
Also, incase you tried out Blackboard you would observe that you get to annotate (draw/write) over live webpages, post which you can take a full page screenshot containing your annotations. So essentially you are not redirected to a new tab in order to draw, but get to live annotate webpages and take the full capture.
The extensions in this genre that I observed so far in chrome web store in its core either:
In Blackboard the idea was to combine best of both worlds, annotate live without switching to a new tab and be able to capture full page screenshot containing your annotations. So that you get the feel of being in a webpage and not an image. I guess that does combine some good features :)
And coming to applications that capture all the good functionalities, suggest you check out the hands-down OG full page screenshot + web annotator -> https://gofullpage.com/ It falls into the 2nd type and implements all important annotation features, and does it right!
Use this extension on chrome, pretty great, it allows you to save file in pdf or jpeg, can automatically scroll and capture whole webpage .
GoFullPage extension on chrome
their website : https://gofullpage.com/