Combining PDFs to 1 File

I am having issues when I combine multiple PDFs into 1 file - the view size does not match. Some pages are much smaller - the goal is to save paper and avoid printing (when I choose print option it looks normal) but to view the pdf as is (if I were to send as is) it's very inconsistant. Can someone help me figure out how to get all pages to be the same size for viewing?