A Study Comparing Upadacitinib (ABT-494) to Placebo and to Adalimumab in Participants With Psoriatic Arthritis Who Have an Inadequate Response to at Least One Non-Biologic Disease Modifying Anti-Rheumatic Drug (DMARD)

The study includes a 35-day screening period, a 56-week blinded period (Period 1), a long-term extension period of up to a total treatment duration of approximately 5 years (Period 2), a 30-day follow-up call or visit, and a 70-day follow-up call. Period 1 includes 24 weeks of randomized, double-blind, placebo-controlled and active comparator-controlled treatment followed by 32 weeks of active comparator-controlled upadacitinib; at Week 24 participants assigned to placebo will be switched to upadacitinib according to their randomization assignment. Participants who meet eligibility criteria will be randomized in a 2:2:2:1:1 ratio to one of five treatment groups: * Group 1: Upadacitinib 15 mg QD * Group 2: Upadacitinib 30 mg QD * Group 3: Adalimumab 40 mg every other week (EOW) * Group 4: Placebo followed by upadacitinib 15 mg QD * Group 5: Placebo followed by upadacitinib 30 mg QD Randomization will be stratified by extent of psoriasis (≥ 3% body surface area \[BSA\] or \< 3% BSA), current use of at least 1 non-biologic DMARD, presence of dactylitis, and presence of enthesitis, except for participants from China and Japan, where randomization for each country will be stratified by extent of psoriasis (≥ 3% BSA or \< 3% BSA) only. Participants who complete the Week 56 visit (end of Period 1) will enter the long-term extension portion of the study, Period 2 (total treatment up to approximately 5 years), and continue study treatment as assigned in Period 1 in a blinded manner until the last subject completes the last visit of Period 1 (Week 56), when study drug assignment in both periods will be unblinded and participants will be dispensed study drug in an open-label fashion until the completion of Period 2. At Week 16, rescue therapy will be offered to participants classified as non-responders (defined as not achieving at least 20% improvement in tender joint count (TJC) and / or swollen joint count (SJC) at both Week 12 and Week 16). Starting at Week 36, participants who fail to demonstrate at least 20% improvement in either or both TJC and SJC compared to Baseline at 2 consecutive visits will be discontinued from study drug treatment. Additionally, in participants continuing on study drug, starting at the Week 36 visit, initiation of or change in background PsA medication(s) is allowed as per local label.