There are certain forms on the IRS website that cannot be downloaded for filing returns. These forms are called "information only forms". Even the photocopy of these forms cannot be used. This is because the original paper forms are machine readable. It has a barcode which the machine will read. If you photocopy it the barcode becomes unidentifiable.
Examples of "information only" tax forms are W2 and W3 series with one or two exceptions; form 1096 and form 8109 B; and the series of 1098, 1099, 5498, and form 5500. Many insurance companies provide assistance in preparing for these forms, so that no errors can be obtained while submitting these forms. They also help to prevent your organization from being penalized for late or incorrect filing of Form 5500. You can find professionals for form 5500 preparation by browsing online.
Thorough knowledge of each of the documents is required if you are filing your tax returns yourself. Improper use of the tax forms may invite fines from the IRS. So if you do not know the proper forms to be used, it is better to seek the assistance of a CPA, an Accountant or an IRS Tax Lawyer. As these are professionals who know the IRS procedures inside out, they will know the proper documents to be used.
While filling the tax forms also care has to be taken. If you don't fill in the details of income correctly, you will end up paying additional taxes or reduced taxes. If you pay less tax than is required to pay, you will be penalized and you will have to pay interest for the outstanding tax.