Choose your source PDFs.
Work with copies. Decide which pages belong in the final document and the order they should appear.
Bring the pages together.
Use the page tools to combine PDFs. Keep the page thumbnails visible so you can see the whole document as you work.
Arrange and check.
Move pages into the order you need. Rotate any that face the wrong way, and remove unwanted pages from the working copy.
Save and reopen the pack.
Save to a new PDF, close it and open the saved file. Check the page count, order and the content of every page.
A useful distinction
Take extra care with forms or documents that already carry certificate signatures. Changing a signed document can affect its signature. Keep the originals and check the final file.
Something different on your screen? Tell us what happened.