If I were you, in such a situation, I would tackle this challenge in layers.
The first thing that I would do is to Preview as much of the document as possible building a general structural understanding of the material and this will help you to promote long term memory.
The next thing that I would do is to Super Read the text to really discern the meaningful gist of the material, followed by a session of Rapid Reading to glean and gain any lost fragments that may be contained in the document that will have pertinence and value.
The more passes you make through the document the more familiar you become with the text. This allows for speed, flexibility and it decreases your stress level when approaching important information because you don't have the "once-through-pass-or-fail" attitude barking down your back. You know you will peel back the document in layers and can rest comfortably knowing your mind will find what is needed through multiple passes.
Just be sure to have a clear, solid purpose in advance to guide you through the process.
