This is a multi-center, randomized, double-blind, double-dummy, active controlled clinical Study. Following a screening period, eligible subjects will be enrolled to an open-label oral IR-LD/CD adjustment period; then an open-label ND0612 conversion period; then after optimization periods subjects will be randomized to receive either ND0612 or its matching Placebo with IR-LD/CD.

Subjects can continue to an optional open-label extension period.

This is a phase III multi-center, randomized, active-controlled, double-blind, double-dummy (DBDD), parallel group clinical trial, investigating the efficacy, safety, and tolerability of continuous subcutaneous (SC) ND0612 infusion in comparison to oral IR-LD/CD in subjects with Parkinson's disease (PD) experiencing motor fluctuations.

This study is comprised of 6 periods:

1. a Screening Period;
2. an open-label oral IR-LD/CD Adjustment Period;
3. an open-label ND0612 Conversion Period;
4. a randomized DBDD active-controlled Maintenance Period;
5. an optional open-label Treatment Extension; and
6. a Safety Follow-up Period.

Inclusion Criteria:

1. Male and female patients, aged ≥30 years.
2. PD diagnosis consistent with the United Kingdom Brain Bank Criteria.
3. Modified Hoehn & Yahr score ≤3 during "ON" state.
4. Average of ≥2.5 hours of OFF time (≥2 hours "OFF" time every day) during waking hours as confirmed by patient diary over 3 days.
5. Taking ≥4 levodopa doses/day (≥3 doses/day of extended release LD/dopa-decarboxylase inhibitor, e.g., Rytary®) at a total daily dose of ≥400mg.

Exclusion Criteria:

1. Atypical or secondary parkinsonism.
2. Severe disabling dyskinesias, based on Investigator's discretion.
3. Previous neurosurgery for PD.
4. Use of duodenal levodopa infusion (LCIG) or apomorphine infusion.
5. Use of the following medications: subcutaneous apomorphine injections, sublingual apomorphine, or inhaled levodopa within 4 weeks.
6. Previous participation in ND0612 studies.
7. History of significant skin conditions or disorders.

Blinded Site Rater, Blinded Clinical Research Associates (CRAs), active drugs and matching placebos are identical in their appearances.