Mock all you want, its well known that teams snoop on each other and anyone that doesn't accept that is just blinkered. After the whole McLaren episode had been put to bed, Autosport ran an article with one of the engineers at Toyota and one at Red Bull, both of whom say they at previous teams have had information on others teams strategies, development etc. Even Nigel Stephney admitted in the trial that Ferrari had info on McLaren, its just that McLaren got caught first.
Oh yes teams have lots of information on their rivals. When I was with Honda we spent so much time analysing other teams, I think it was to the detriment of the car's performance. For example from video and audio clips it is possible to determine a rivals engine mapping, very useful information.
Now the question from your statement is, do teams have full design documents that have been stolen from the other team? Are these physical documents or just information they have gained from looking at what is available in the public domain?