Cut (split) double pages

I had a similar problem with a pdf file composed of scanned images of a hard copy document that was originally 8.5x11 inch pages. The pdf pages had four images/pages of the document, making each pdf page 17x22 inches. My solution (in Windows):
1. Make a copy of the original and place the copy in a separate/new empty folder. This safely preserves the original.
2. Switch to the new folder.
3. Open the copied file and open the Page Thumbnails panel.
4. Ensure all pages have the appropriate left/right and upright orientations. Save your work without exiting.
5. Extract/remove/save any non‐dual pages and non‐uniform sized pages to separate files. For example, assume the file will contain only 11x17 inch pages that will be split into 8.5x11 inch pages.
6. Save your work, exit the file, and return to the folder.
7. Change the copied file’s name to a short and easy name (e.g., “test‐l.pdf”). This file will be used for left side pages (generally even numbered).
8. Copy the “test‐l.pdf” and change its name to “test‐r.pdf”. This file will be used for right side pages (generally odd numbered).
9. Open the “test‐l” file.
10. Open the Page Thumbnails panel.
11. Use the Crop tool to open the Set Page Boxes popup. The box’s window and caption indicates the page’s (cropped) image and dimensions.
12. Set the Right: crop value as desired. For example, for 17 inch wide pages, set the Right: crop value to 8.5 in. Leave the other crop values as 0 in.
13. Set the Page Range to All and select OK. After cropping completes, save your work without exiting.
14. Use Extract Pages… to save all pages separately for recombining later.
a. Open the Extract Pages popup box.
b. Set the Pages: range to the appropriate range. For example, 1‐10 for a ten page pdf file.
c. Check the Extract Pages As Separate Files box.
d. Select OK. The extracted page files will have the page position appended to the “test‐l” name.
15. Close the “test‐l” file.
16. Repeat steps 9 through 15 for the “test‐r” file, this time setting the Left: value to 8.5 in and leaving the other crop values as 0 in.
Combine the individual page files into one pdf file. For few files, this may be as simple as:
 Opening the first page file via the folder window, opening the Page Thumbnails panel, and dragging/dropping the remaining files from the folder, or
 Using File>Combines Files into a Single PDF…, and
 Arranging the page order as required.
For a very large number of files, it is helpful to use a Windows level utility to bulk rename the individual files to “pg001”, “pg002”, etc…, where the right side pages are odd‐numbered and the left side pages are even‐numbered and can be sorted in page order.

Duplicate the pages and use the crop tool in Acrobat. After this merge odd and even pages.