S-corporation
https://www.irs.gov/pub/irs-pdf/f1120ssk.pdf
https://www.irs.gov/pub/irs-pdf/i1120ssk.pdf
Partnership
https://www.irs.gov/pub/irs-pdf/f1065sk1.pdf
https://www.irs.gov/pub/irs-pdf/i1065sk1.pdf
Trust
https://www.irs.gov/pub/irs-pdf/f1041sk1.pdf
https://www.irs.gov/pub/irs-pdf/i1041sk1.pdf