Ger: Beyond the basics, which I think you have defined pretty well, it would be helpful if you could provide a price point that you might like to stay below and a few other personal preferences beyond simple weight.
In the meantime, there are a few tabletPCs that might work for you. On the lower end of the cost scale, there is the Dell Duo (which I've handled and which didn't strike me as weighing 3.5 lbs...?!??), the Fujitsu Q550 and the HP Slate 500. The Dell Duo is touch only, but the Q550 and the Slate 500 feature pen and touch. All are under $1000 new. In addition, you can look for many older models of tablets on sites like eBay; both convertibles (screen + keyboards) and slates (screen only with virtual (onscreen) keyboards). Companies like Dell also offer refurbished tablets like the XT2, which is a powerful Core 2 Duo model, for just around $1000. Refurbished hardware typically looks new and can be a great value: http://www.dell.com/us/dfb/p/latitude-xt2/pd
Above $1000 there are several nice options. The Asus EP121 is both powerful and reasonably light at about 2.5 lb. The brand new Samsung Series 7 Slate is even more powerful yet lighter at about 2 lbs. Fujitsu, Lenovo and others also offer powerful convertibles convertibles in the $1500 to $2000+ range.
All of these devices run Windows and are perfectly capable of running Office and Acrobat.
Without knowing more, I would tentatively recommend the Asus EP121 ( http://www.amazon.com/ASUS-Slate-EP1...8025602&sr=8-1 ). You can see that its owners rate it very highly. I own several slates but I have to admit that I also prefer my EP121.
Hopefully, other forum members will chime in with their thoughts as well. In the meantime, continue doing research; this is actually a great time to get into tablets!