There was a time when buying snapped/old expired domains with a lot of backlinks and just 301-redirect them to your website was a thing.
This was risky, black hat and no longer work. Non-expired domains is another story - quote from Matt Cutts:
There are some domain transfers ( e.g. genuine purchases of companies) where it can make perfect sense for links to transfer. But at the same time it wouldn’t make sense to transfer the links from an expired or effectively expired domain, for example. Google (and probably all search engines) tries to handle links appropriately for domain transfers.
The sort of stuff our systems would be designed to detect would be things like someone trying to buy expired domains or buying domains just for links.
So Google may transfer PageRank when company A is acquiring company B and the two websites merges.
What about websites that isn't owned by any company and just run by a private individuals?
For example: A big backcountry skiing e-commerce website with thousands customers each month is looking for ways to increase it's backlink profile. There happens to be a blogger that have a great "avalanche information and risks"-website. Frequent updates, great content (that would interest many customers) and excellent and strong backlinks from many high authority domains.
If the e-commerce website would purchase the blog, move all content to their website and make corresponding 301-redirects - would that be considered a genuine domain transfer?
And could this be scaled - there might also be a great blog about backcountry skiing history, a backcountry skiing gear review website, a website with a interactive map - featuring the best backcountry skiing destinations to visit. Would acquiring those websites most likely pass PageRank?
Update: I am interested in how Google theoretical can differentiate between
company A purchasing and merging
company B, versus
company A purchase and merging highly relevant
blog B and
blog C. Would the blogs likely pass PageRank or not?