Bosc is considered a winter pear and will not ripen on the tree. If they do, they will be overripe. They should be ready to pick if when slightly lifted, the stem comes away from the tree easily. Or when the tip of the stem end has a slight give to it.

They can be stored then in a cold, dark location or allowed to ripen on the counter at room temp for several days. I'd keep them out of the sun!

Bosc is considered a winter pear and will not ripen on the tree

Yep. And not the only European pear variety that is ripened in storage rather than on the tree - this requirement is not that unusual with these.

Here's a good article on how Bosc and Comice pears are ripened.

But; I like this web page for its description of when a pear is ready to eat. Myself; I prefer a pear that's considered over ripe. Sweet and juicy