Firms should file Form ITR-3 or ITR-4-Sugam for income tax. Partnership and LLP ITRs should be Form-5. Companies should file Income Tax Returns using Form ITR-6. For charitable trusts, file Form ITR-7. For Tax Audit, returns must be digitally signed. LLPs and companies must do it. Otherwise, you can use Aadhar or net banking for E-Verification. You can also sign and send the ITR-V (Ack) to CPC for processing.