Here's a real timesaving process that's terrific for visual people. Rather than combining document content through dialogs, you can do it visually using the Pages pane.
Start with two documents, one to which you want to add pages (the recipient) and the other from which you're taking pages (the donor).
With both documents open, choose Window > Tile > Horizontally. The two document windows display in a stack on the screen.
Click the Pages tab on each document to open it and generate thumbnails. Drag the right margin of the Pages pane to the right to display the largest possible number of page thumbnails.
Note: You can drag the Pages pane to fill the entire screen, but in a very large document you still won't see all the thumbnails in the document.
Stack the two documents on top of each other. In these documents, the Pages panes are enlarged to show several thumbnails.
Select the page thumbnails from the donor document.
You can select multiple page thumbnails.
Drag the thumbnails from the donor document's Pages pane to the recipient document's Pages pane. You see a heavy black line at the position of the pointer.
When you drag thumbnail images from one document to another, you see a heavy black line between the thumbnails at your pointer's position.
When you're in the right spot, release the mouse. Acrobat adds the page thumbnails to the Pages pane and the pages themselves to the document. The original donor document is unaffected.
The page thumbnails are added to the Pages pane and the pages are added to the document.
Organize and arrange the pages as desired. Save the file, and then close the donor document.
Dialog or Drag and Drop?
Some people aren't comfortable unless they can see page numbers, file names, and so on. If this is you, by all means use the dialog boxes for adding content from one document to another. For you more visual people, the sky is the limit?well, actually, the screen is the limit. You can readily display the Pages panel from two, three, or even more documents on the screen and drag pages between the documents. Visually combining documents works best when the content is visual. For example, a long report that contains very little except text is difficult to work with if you're relying on thumbnails. On the other hand, if you are working with large images or slideshow pages, the process works very well.
OK, so you want to stamp your document. Maybe you need to give reviewers some advice about the document's status or sensitivity. This tip from author Ted Padova demonstrates how to add stamps with the Stamp Tool along with related comments.