A frequent question is: How do I import or place one InDesign document into another to combine them?
Excellent question, but you don’t start from import or place.
Open both the source and destination document in InDesign, and tile the two windows. Now, in the Pages palette of the source document, whose pages you want to place in the other, select all the pages (click on the first, SHIFT-click on the last), and then drag the icons from the Pages palette and drop them into the destination document. Bing, bang, boom! Two documents, now merged.