Insert From PDF... (Edit/Pages menu)
Select Pages to access the Insert from PDF... command, as below:
Use this command to insert pages from one PDF to the one currently opened. Once selected, this command will let you browse for and open the PDF containing the pages you need.
After opening your file, the Insert Pages From PDF dialog will appear where you can then specifiy the page or range of pages you want to insert into the current PDF.
In the Before Page field, designate where in the PDF you wish to insert the selected pages. Click on Insert and your pages will be inserted automatically into the PDF. Save the PDF to finalize your changes.