A Study to Learn About Study Medicine Called PF-08634404 as a Single Treatment and Combination Treatment in Adult Participants With a Liver Cancer Called Hepatocellular Carcinoma, That is Too Advanced to be Removed by Surgery and May Have Spread to Other Parts of the Body.

Inclusion Criteria: * 18 years of age or older at screening. * Locally advanced or metastatic HCC with diagnosis confirmed by histology/cytology or clinically by AASLD criteria (for patients with cirrhosis). Participants without cirrhosis require histological confirmation of diagnosis. * Disease that is not amenable to curative surgical and/or locoregional therapies, or progressive disease after surgical and/or locoregional therapies. * At least 1 measurable (as defined by RECIST 1.1 per investigator) and untreated lesion. * Adequate hepatic, liver, and renal function * No prior systemic therapy for HCC. * ECOG performance status 0 or 1 * Child-Pugh Class A Key Exclusion Criteria: * Moderate or severe ascites. * History of hepatic encephalopathy. * Participants with known active CNS lesions, including leptomeningeal metastasis, brainstem, meningeal, or spinal cord metastases or compression. * Clinically significant risk of hemorrhage or fistula. * Participants with any history of another malignancy within 3 years. * History of allogeneic organ transplantation and allogeneic hematopoietic stem cell transplantation. * Participants with active autoimmune diseases requiring systemic treatment within the past 2 years. * Clinically significant cardiovascular disease within 6 months prior to the first dose. * Major surgery or severe trauma within 4 weeks prior to the first dose or planned major surgery during the study. * History of severe bleeding tendency or coagulation dysfunction. * History of severe ulcers, unhealed wounds, gastrointestinal perforation, abdominal fistula, gastrointestinal obstruction, intra-abdominal abscess, or acute gastrointestinal bleeding, including bleeding event due to esophageal and/or gastric varices, within 6 months prior to the first dose. * Participants with acute, chronic or symptomatic infections. * Participants with history of immunodeficiency.