Inclusion Criteria:

          1. Be willing and able to provide written informed consent/assent for the trial.

          2. Histologically confirmed metastatic pancreatic ductal adenocarcinoma, via archived or
             fresh core biopsy of either primary tumor or metastatic site.

          3. Available tumor tissue (formalin-fixed paraffin-embedded [FFPE] block preferred) with
             enough tumor to make a minimum of 5-10 unstained, consecutive FFPE slides (10 slides
             are preferred) of 1 archival block that meets specific tissue sample requirements.
             Archived or fresh tissue from the primary lesion or a metastatic lesion is required.
             Note: Fine needle aspirates or brushing biopsies will not be acceptable. This tumor
             tissue requirement is for the determination of the HA-high or -low expression status.

          4. Subjects must be determined to be HA-high based on archival or fresh tumor biopsy that
             meets the requirements noted in the previous inclusion criterion.

          5. 18 years of age on day of signing informed consent.

          6. Have measurable metastatic disease based on RECIST 1.1.

          7. Life expectancy ≥ 12 weeks.

          8. Have a performance status of 0 or 1 on the ECOG Performance Scale.

          9. Received no more than 2 prior lines of systemic therapy for metastatic disease (1 or 2
             prior lines of therapy for metastatic disease are allowed)

         10. Be willing to provide tumor tissue from newly obtained tumor cores or excisional
             biopsy for research purposes. Newly-obtained is defined as a specimen obtained within
             2 weeks (14 days) prior to initiation of treatment on Day 1.

         11. Be willing to provide tumor tissue from tumor biopsy after 6 weeks of treatment
             (mandatory, if safe and feasible), and at the time of tumor progression (optional, if
             safe and feasible). Note: Fine needle aspirates or brushing biopsies will not be
             acceptable.

         12. Demonstrate adequate organ function, all screening labs should be performed within 14
             days of treatment initiation.

         13. Female subjects of childbearing potential should have a negative urine or serum
             pregnancy within 72 hours prior to receiving the first dose of study medication. If
             the urine test is positive or cannot be confirmed as negative, a serum pregnancy test
             will be required.

         14. Female subjects of childbearing potential must be willing to use an adequate method of
             contraception for the course of the study through 120 days after the last dose of
             study medication.

             Note: Abstinence is acceptable if this is the usual lifestyle and preferred
             contraception for the subject.

         15. Male subjects of childbearing potential must agree to use an adequate method of
             contraception starting with the first dose of study therapy through 120 days after the
             last dose of study therapy.

             Note: Abstinence is acceptable if this is the usual lifestyle and preferred
             contraception for the subject.

         16. No history of acute DVT/PE or CVA/TIA (new within 4 weeks of study registration) or
             clinical significant carotid artery disease.

         17. If prior history of DVT/PE the patient needs to be on stable doses of anticoagulation
             with low molecular weight heparins.

               -  Patients should have all eligibility criteria met, before undergoing the baseline
                  research biopsy.

        Exclusion Criteria:

          1. Is currently participating and receiving study therapy or has participated in a study
             of an investigational agent and received study therapy or used an investigational
             device within 2 weeks of the first dose of treatment.

          2. Has a diagnosis of immunodeficiency or is receiving systemic steroid therapy
             (equivalent of > 20 mg of hydrocortisone per day) or any other form of
             immunosuppressive therapy within 7 days prior to the first dose of trial treatment.

          3. Has a known history of active tuberculosis (TB).

          4. Hypersensitivity to pembrolizumab or any of its excipients.

          5. Known allergy to PEGPH20 (hyaluronidase).

          6. Current use of megestrol acetate (use within 10 days of Day 1).

          7. Contraindication to heparin as per institutional guidelines.

          8. Has had a prior anti-cancer monoclonal antibody (mAb) within 4 weeks prior to study
             Day 1 or who has not recovered (i.e., ≤ Grade 1 or at baseline) from adverse events
             due to agents administered more than 2 weeks earlier.

          9. Has had prior chemotherapy, targeted small molecule therapy, or radiation therapy
             within 2 weeks prior to study Day 1 or who has not recovered (i.e., ≤ Grade 1 or at
             baseline) from adverse events due to a previously administered agent.

               -  Note: Subjects with ≤ Grade 2 neuropathy are an exception to this criterion and
                  may qualify for the study.

               -  Note: If subject received major surgery, they must have recovered adequately from
                  the toxicity and/or complications from the intervention prior to starting
                  therapy.

         10. Has a known additional malignancy that is progressing or requires active treatment.
             Exceptions include basal cell carcinoma of the skin or squamous cell carcinoma of the
             skin that has undergone potentially curative therapy or in situ cervical cancer.

         11. Has known active central nervous system (CNS) metastases and/or carcinomatous
             meningitis. Subjects with previously treated brain metastases may participate provided
             they are stable (without evidence of progression by imaging for at least four weeks
             prior to the first dose of trial treatment and any neurologic symptoms have returned
             to baseline), have no evidence of new or enlarging brain metastases, and are not using
             steroids for at least 7 days prior to trial treatment. This exception does not include
             carcinomatous meningitis which is excluded regardless of clinical stability.

         12. Has active autoimmune disease that has required systemic treatment in the past 2 years
             (i.e. with use of disease modifying agents, corticosteroids or immunosuppressive
             drugs), or documented history of clinically severe autoimmune disease (e.g., colitis,
             Crohns' disease)*. Replacement therapy (eg, thyroxine, insulin, or physiologic
             corticosteroid replacement therapy for adrenal or pituitary insufficiency, etc.) is
             not considered a form of systemic treatment.

             *Any relevant diseases that are not listed as examples of exclusionary diseases are to
             be discussed with the Sponsor-Investigator.

         13. Has known history of, or any evidence of active, non-infectious pneumonitis.

         14. Has a history of (non-infectious) pneumonitis that required steroids or has current
             pneumonitis.

         15. Has known hepatobiliary diseases (e.g., primary biliary cholangitis, primary
             sclerosing cholangitis, immune mediated cholangitis); patients with cholangitis
             attributed to infectious etiology (e.g., ascending cholangitis, bacterial cholangitis)
             are eligible if the infection has been fully recovered prior to the screening visit.

         16. Has known history of drug-induced hepatobiliary toxicities

         17. Has an active infection requiring systemic therapy.

         18. Has a history or current evidence of any condition, therapy, or laboratory abnormality
             that might confound the results of the trial, interfere with the subject's
             participation for the full duration of the trial, or is not in the best interest of
             the subject to participate, in the opinion of the treating investigator.

         19. Has known psychiatric or substance abuse disorders that would interfere with
             cooperation with the requirements of the trial.

         20. Is pregnant or breastfeeding, or expecting to conceive or father children within the
             projected duration of the trial, starting with the pre-screening or screening visit
             through 120 days after the last dose of trial treatment.

         21. Has received prior therapy with an anti-PD-1, anti-PD-L1, or anti-PD-L2 agent, or any
             other immune checkpoint inhibitors.

         22. Has received prior therapy with PEGPH20, or has participated in the Halozyme HALO 301
             phase III study.

         23. Has a known history of Human Immunodeficiency Virus (HIV) (HIV 1/2 antibodies).

         24. Has known active Hepatitis B (e.g., HBsAg reactive) or Hepatitis C (e.g., HCV RNA
             [qualitative] is detected).

         25. Has received a live vaccine within 30 days of planned start of study therapy. Note:
             Seasonal influenza vaccines for injection are generally inactivated flu vaccines and
             are allowed; however intranasal influenza vaccines (e.g., Flu-Mist®) are live
             attenuated vaccines, and are not allowed.