You can easily merge PDFs from your phone's file manager by following these steps:

1. Open Zoop Wallet, tap on 'PDF Tools,' and select 'Merge PDFs' from the Home screen.  
(You'll see a guide explaining the merge feature.)

2. Tap on 'Select Documents' and choose 'Files' to navigate to your phone's file manager.

3. Select the PDFs you want to merge.
(Make sure to choose more than one PDF.)

4. If you want to add more PDFs, tap the '+' icon and select additional files from either your phone or Zoop Wallet.

5. Re-arrange the selected PDFs if needed, and preview them before merging.

6. Tap 'Continue,' rename the file if necessary, add tags, and select where you want to store the document (either in your profile or a family member's profile if applicable).  

(If you want to save PDFs selected from your file manager into Zoop Wallet, tick the option to save them in the 'Others' category.)

7. Tap 'Merge PDFs' to complete the process.

Your merged PDF will be saved in the 'Others' category.