How to condense a full journal paper to a two-page conference abstract?
The usual advice for this type of question is:


  Do not shorten, but rewrite.


This will not only produce a smoother text, but also will be quicker. Squeezing eight pages to two is a tremendous headache and time consuming. Usually it also results in an awkward text. Writing two pages for something that you understand thoroughly is quicker. Make a good plan what you want to tell in two pages and write the two pages from scratch.

Edit: I just saw, that this advice is the same as the most upvoted comment for this question. In essence, this question is a duplicate…