PCT(Patent Cooperation Treaty)
The international application system is a system in which an applicant may submit a PCT international application to the Patent Office (Receiving Office) of which the applicant is a national or resident, and within a predetermined period from the filing date, such an application may be filed as a national-phase application with the national Patent Offices of countries (designated or selected countries) where the applicant wants to obtain a patent. The filing date of the PCT international application shall be accepted as the filing date of the designated countries.
However, in a case where a PCT international application is filed with the claim of priority based on a prior application, such an application must be filed within 12 months from the filing date of the prior application so that the priority can be accepted.

PCT
International Application

When an applicant submits three copies of application documents prepared in the Korean language, English language or Japanese language to the Receiving Office, formality examination is conducted (necessary documents are the same as those of a domestic application).
The designation of countries: There is an effect to designate all PCT member countries entered into the Patent Cooperation Treaty at the time of filing an international application (However, an intention whether or not to designate Germany, Japan or Korea can be separately indicated.)
International Publication by WIPO: In general, the WIPO publishes an international application when 18 months from the priority date has passed, and if an applicant demands to publish his or her international application to the WIPO, the international application may be published early.

Progress of Examination

Each designated Office which receives a translation submitted by an applicant shall examine the application corresponding to the translation according to each law of the designated countries and decide whether or not to grant a patent.
The PCT international application system adopts the reach doctrine in which the date when a document reaches the WIPO is actually deemed the receipt date. It is possible to delete any designated country, but impossible to add it.