Designate 'catcher' for selections

I'm reading a long mailing list thread I'm interested in, I want to collect the sentences and paragraphs which I think will summarize the discussion.

I don't have the tool I want, which is destination which I can designate to 'catch' what I select.

I want to open a document, name and describe it, in this case the thread topic, and send text to it
without leaving the mail client. Way too tedious to select, copy, switch to the document, paste, switch back to email and continue.

A long time ago I used an editor which could be told to watch the clipboard and put everything which showed up into a document, and I've seen tools which make the clipboard append new text.

Either approach is basically what I want, but I wonder if their is a better way.

Sources of content

- browser
- pdf files
- other documents

I think most would come from a browser.