Open the PDF in Acrobat DC, and then choose Tools > Organize Pages or choose Organize Pages from the right pane. The Organize Pages toolset is displayed in the secondary toolbar.
In the secondary toolbar, click Replace. The Select Files With New Pages dialogue box appears.
Select the document containing the replacement pages, and click Open.
Under Original, enter the pages to be replaced in the original document.
Under Replacement, enter the first page of the replacement page range. The last page is calculated based on the number of pages to be replaced in the original document.
The Organize Pages toolset is displayed in the secondary toolbar.
