Those of us with LDD/ADD know how it feels to lose important papers because we have shoved them in the most convenient place at the time of receiving them. This stress is easily avoidable.

Very simply, O.H.I.O.; this stands for: Only Handle It Once. As soon as you receive loose papers, put them in their permanent home.
“For people with ADD, TO DO piles might just as well be called NEVER DONE piles” (Hallowell, E. and Ratley, J. 1994). These TO DO piles only seem to be a constant source of guilt; reminding us of how irresponsible and unorganized we are.

Get the habit of finding permanent homes for any paperwork that is given to you, for that matter, any paperwork at all. If you cannot immediately find a home for the paperwork in question, you might as well throw it away. At least by throwing it away, you are aware that YOU are the cause of not knowing the information, not the situation (which arises, due to misplacing the paperwork.