The following documents will guide you in formatting papers in APA style (in both Word 2013 and 2016, as well as in Google Docs) with a different header on page 1 than throughout the rest of your paper, and with proper page number formatting. The first document bulleted below shows how to do so with screen shots taken from Word 2016, the second with screenshots taken from Word 2013, and the third using screenshots taken from Google Docs.
The fourth document walks you through how to divide your Word doc into sections, allowing you to use different headers and different page number formats within each (such as Roman numerals in one section and Arabic numerals in another, all contained in one Word file).
(Following these guidelines will save you a lot of headaches, allowing you to save your correctly-formatted paper in one single file.)
According to the APA,
A digital object identifier (DOI) is a unique alphanumeric string assigned by a registration agency (the International DOI Foundation) to identify content and provide a persistent link to its location on the Internet. The publisher assigns a DOI when an article is published and made available electronically.