Part A: - Participants assigned male or female at birth who are of childbearing potential and engage in heterosexual intercourse must agree to use protocol-specified method(s) of contraception. - Have a body mass index (BMI) of ≤ 30.0 kg/m2 at screening and at admission. Part B: - Participants assigned male or female at birth who are of childbearing potential and engage in heterosexual intercourse must agree to use protocol-specified method(s) of contraception. - Chronic hepatitis delta (CHD) for ≥ 6 months prior to screening, documented by prior medical history. - Must be receiving a commercially available entecavir, TAF, or TDF for the treatment of hepatitis B virus (HBV) infection at or prior to enrollment. Coformulation as part of a fixed-dose combination for the treatment of HIV is permitted. - Non-cirrhotic or compensated cirrhosis. - Hepatitis delta virus ribonucleic acid (HDV RNA ) > 100 IU/mL at screening. - Alanine aminotransferase (ALT) level > 1 × Upper limit of normal (ULN), but < 10 × ULN at screening.

Part A: - Positive serum or urine pregnancy test. - Participants with plans to breastfeed during the study period. Part B: - Positive serum or urine pregnancy test. - Participants with plans to breastfeed during the study period. - Current or previous clinically decompensated liver disease, including coagulopathy, hepatic encephalopathy, and esophageal varices hemorrhage due to HDV or HBV. - Child-Turcotte-Pugh (CTP)-B or -C or a CTP score of ≥ 7. Note: Other protocol defined Inclusion/Exclusion criteria may apply.