Entering US with a K-3 does not mean that you are a permanent resident of US. You have to submit the application of status adjustment once you enter US with the approval of immigration application.

No. K visa is only available for the spouse/fianc(e)e and child of a US citizen. The spouse/fiance(e) and child of a permanent resident can apply for V visa to enter US before getting the immigration visa.

Spouse means lawful husband or wife. In order to successfully petition for an immigrant visa for your spouse, your relationship with your spouse must be established and your spouse must be admissible to the United States under the immigration law.

First, K-1 is for the fiance of a US citizen, and K-2 is for the person who is under 21 years of age and is the unmarried child of an alien eligible to be a K-1. K-3 is for the spouse of a US citizen, and K-4 is for the person who is under 21 years of age and is the unmarried child of an alien eligible to be a K-3.

Second, K-1/2 visa is one entry visa, while K-3/4 is multi-entry visa. The fiance with K-1 must marry with the US citizen in 3 months after entering US. The K-3 holder can go in and out of US freely without advance parole even during the adjustment period..

It is a new nonimmigrant category within the immigration law that allows the spouse or child of a U.S. citizen to be admitted to the United States in a nonimmigrant category. The admission allows the spouse/ fiance or child to complete processing for permanent residence while in the United States. It also allows those admitted in the new category to have permission for employment while they await processing of their case to permanent resident status.