Salesforce offers both Platform Developer I (PD-I) and Platform Developer II (PD-II) Certification Exams, assessing the development knowledge of custom applications in the candidate. But one differentiates from the other can be identified through these points:
The Platform I and II certifications can be distinguished by the individual's knowledge level, i.e. Beginners or Experienced. While in PD-I, assessment questions are more straightforward than in PD-II, which contains more complex and scenario-based questions.
PD-I is an entry-level certification that any individual knowing the concepts of Developer can attempt. But when appearing in the PD-II certification exam, one should have at least 2-3 years of Development experience in the Salesforce ecosystem.
PD-I is a prerequisite certificate for appearing in PD-II.
PD2 is a combination of the Certification exam, inclusive of 3 super badges on the Trailhead. This way, while earning the Platform Developer II Certification, you will also get entitled to 3 Super Badges on Trailhead. You can complete the trails over Trailhead for the following super badges:
Apex Specialist
Data Integration Specialist
Advance Apex Specialist