Puerto Rico is a US territory, and US Visa Policy also applies to Puerto Rico visa policy. It means you can apply for a US visa for travelling to Puerto Rico. There is no separate (individual) visa for Puerto Rico. All the rules valid for the US visa are also applicable to Puerto Rico.
For detailed information about US visas, you can check US Visa Policy.
Nationals who are eligible for US Visa Waiver Program are not required to apply for a visa to travel to the USA or Puerto Rico, but they have to obtain Electronic Authorization (ESTA) if they are arriving by air or sea. Visitors can stay for up to 90 days in the USA or Puerto Rico.
Electronic System for Travel Authorization is not considered as a visa, but it is a prerequisite for entering the USA by air or sea. You can apply for an ESTA from this website. ESTA fee is 4 USD, and if your application is approved, then you will be charged an additional 10 USD.
US citizens travelling to Puerto Rico are not required to carry a passport, the government-issued photo ID is enough for them to enter Puerto Rico.
Yes, you can travel to Puerto Rico with a US visa. Puerto Rico is a US territory and US Visa Policy also applies to Puerto Rico visa policy.
No, Schengen visas are not valid for traveling to Puerto Rico.
No, Canada visas are not valid for traveling to Puerto Rico.
No, Puerto Rico doesn’t have its own visa policy. Puerto Rico is a US territory and US Visa Policy also applies to Puerto Rico visa policy. It means you can apply for a US visa for traveling to Puerto Rico. There is no separate (individual) visa for Puerto Rico.
Your passport must be valid until your departure date from Puerto Rico, but it is advisable to possess a passport valid for at least the next six months for avoiding any issues.