A Study of JNJ-73763989 + Nucleos(t)Ide Analog in Participants Co-Infected With Hepatitis B and Hepatitis D Virus

Inclusion Criteria: * Medically stable based on physical examination, medical history, vital signs, electrocardiogram (ECG) at screening * Chronic hepatitis B virus (HBV) and hepatitis D virus (HDV) co-infection with documentation at least 6 months prior to screening * For Part 1: hepatitis D RNA (HDV RNA) greater than or equal to (\>=) 1000 international units per milliliter (IU/mL) at screening. For Part 2: must have HDV RNA values \>= 500 IU/mL, and must have hepatitis B surface antigen (HBsAg) values less than or equal to (\<=) 10000 IU/mL at screening or HDV RNA values at screening are \<= 100000 IU/mL * Alanine aminotransferase (ALT) greater than upper limit normal (ULN) but less than 10 times (ULN) * Body mass index (BMI) between 18.0 and 35.0 kilogram per meter square (kg/m\^2), extremes included * Highly effective contraceptive measures in place for female participants of childbearing potential or male participants with female partners of childbearing potential * Non-cirrhotic participants and participants with compensated cirrhosis (Child Pugh class A) at screening (Part 1) and participants must have absence of cirrhosis and platelet count of \>= 140000 per deciliter (dL) for enrollment into Part-2 Exclusion Criteria: * Evidence of infection with hepatitis A, C, or E virus infection or evidence of human immunodeficiency, virus type 1 (HIV-1) or HIV-2 infection at screening * History or evidence of clinical signs/symptoms of hepatic decompensation including but no…