We will export the pdf file after finishing the typesetting in indesign. There are two kinds of pdf files, for printing and web.
For web: the size of pdf file will not very large. So we just ensure the text and the picture can be look clearly.
For printing: then it requires a relatively high accuracy of the source file. But there will be so many problem to somebody in seting up the expert of pdf. Now I wil try to explain it in detail and hope it will help you.
First, there are two kinds of method to open the exporting pdf menu: File > Export or Ctrl + E