The areas that I have focused the most are typically around the following:
1. Finance (accounting, tax, etc)
2. Legal – Litigation (any litigation pending)
3. Legal Corporate structure (subsidiaries and legal entities)
4. IT (Data Privacy and Security and existing contracts)
5. Product (Whatever the company is being acquired for, all relevant information related to that company or product)
6. HR – If we plan to retain employment for the target company, we request HR related information near the end of due diligence to ensure we are ready for day 1 integration (ie. comp as we will need to do a market assessment on compensation and provide welcome letters to employees, this is also used to adjust payroll costs in the model).