Yes, put in an offer and make it contingent upon a satisfactory review of all lease agreements and also on receiving an estopel certificate from each tenant.
Has the seller provided ANY information? They should have some basic income statements in regard to what the building generates- you should be careful about what's in there.
Things to look for in addition to the income are whether or not the leases are NNN or Gross, what expenses the building generates, what expenses the landlord is responsible for, etc. Even if they are NNN you should have a good handle on the expenses, since you will be paying those expenses in the event of vacancy. Landlords often fudge expenses, you need to get a good feel for what it will actually cost. You may be able to save money on the expenses or you may have higher expenses.
I have seen landlords run their buildings into the ground, so a new owner has to spend $100,000 to fix the building up. I have a good example where this happened and the building was near vacant when it was sold, the buyer dumped a bunch of cash into the building and now it's near full. On the other hand, I've seen buyers who look at NNN leases and think there's no reason to reduce building costs because the tenants pay those costs. Well, if you save the tenants money on the NNN expenses, they can afford to put more into the base rent. Then if you get caught holding vacant space, you are also doing so at a lower cost...
As for the NDA/Confidentiality Agreement, you could sign one if they request but they probably won't. If you do, you should abide by it, but I haven't seen many that actually had real teeth.
This is all just my opinion and no legal advice is being presented here. Seek legal counsel.