Study to Assess Change in Disease Activity and Adverse Events of Oral Upadacitinib Compared to Subcutaneous Adalimumab in Adult Participants With Moderate to Severe Rheumatoid Arthritis

* Diagnosis of Rheumatoid Arthritis (RA) for \>= 3 months based on the 2010 American College of Rheumatology/European Alliance of Associations for Rheumatology (ACR/EULAR) classification criteria for RA. * Treated for \>= 3 consecutive months prior to screening with 1 tumor necrosis factor inhibitor (TNFi) (only 1 of originator or biosimilar certolizumab pegol, etanercept, golimumab or infliximab) for RA, but continue to exhibit active RA, or had to discontinue due to intolerability or toxicity, irrespective of treatment duration. Up to 15% of participants who were intolerant to 1 TNFi will be allowed to enroll. Prior administration of different biosimilar versions for the same originator TNFi or switching between originator and biosimilar version of the same originator TNFi are acceptable. Cycling between biosimilars of different originator TNF inhibitors is not acceptable. * On oral or parenteral methotrexate (MTX) therapy \>= 3 consecutive months and on a stable prescription of 15 to 25 mg/week (or \>= 10 mg/week in participants intolerant of MTX at doses \>= 15 mg/week) for \>= 4 weeks prior to the first dose of study drug. In addition, all participants should take a dietary supplement of folic acid or folinic acid throughout the study participation. * For a Chinese, Japanese, Korean, or Taiwanese participant, a stable dose of MTX \>= 7.5 mg/week is acceptable. * Additional local requirements for MTX may apply. * Meets both of the following disease activity criteria: * \>= 6 swollen joint (based on 66 joint counts) and \>= 6 tender joints (based on 68 joint counts) at screening and baseline; * High-sensitivity C-reactive protein (hsCRP) \>= 3 mg/L (central lab, upper limit of normal \[ULN\] 2.87 mg/L) at screening.

* History of any arthritis with onset prior to age 17 years or current diagnosis of inflammatory joint disease other than Rheumatoid Arthritis (RA). * Prior exposure to any janus kinase (JAK) inhibitor. * Prior exposure to adalimumab (original or biosimilar) or to any approved or investigational TNF inhibitor other than infliximab, etanercept, certolizumab pegol and golimumab. * Prior exposure to an approved or investigational non-TNFi biologic disease modifying anti-rheumatic drug (bDMARD) or targeted synthetic disease modifying antirheumatic drug (tsDMARD).