In Acrobat (not Reader), open all the documents you want to consolidate and make sure to open the Thumbnails pane. You can then simply drag a Thumbnail from one pdf document to the other document's thumbnail pane into the desired page position. Or you can rearrange the page order after you pulled the the pages into one document. This trick works well when you want to combine only certain pages from 2 or more pdf files with multiple pages. Example, page 2 from one pdf and page 6 from another. Then save. Simple as that.