• Male and female subjects aged 18-75 years (including 18 and 75 years).

• Pancreatic ductal adenocarcinoma confirmed by pathology (histology) or cytology.

• Patients with metastatic pancreatic ductal adenocarcinoma.

• At the time of study enrollment, according to the solid tumor efficacy evaluation criteria (RECIST1.1), imaging diagnosis had at least one measurable lesion (lesion diameter ≥10 mm and lymph node diameter ≥15 mm according to CT or MRI evaluation).

• Physical condition score ECOG score 0-2 points.

• Expected survival ≥ 12 weeks.

• Major organ function is normal.

• The AE caused by previous anti-tumor therapy must be restored to the level of ≤ grade 1 (CTCAE v5.0) or the level specified in the inclusion criteria. If the investigator determines that NCI-CTCAE≤ grade 2 and there is no safety risk to the subject, the participant can be enrolled, such as receiving immune checkpoint inhibitor therapy. Subjects with type 1 diabetes and hypothyroidism that are stable after hormone replacement therapy.

• Fertile female subjects must undergo a serum pregnancy test within 7 days before the first dose, and the result is negative; And must be non-lactating. Fertile female subjects and male subjects whose partners are women of reproductive age must agree to comply with the contraceptive requirement from the time of signing the informed consent until 30 days after the final administration of the trial drug (for subjects receiving HRS-4642);

⁃ The subjects voluntarily joined the study and signed the informed consent, with good compliance and follow-up.