Hi there
I hope you're doing well! Thank you for reaching out.
If you want to open a file offline, you need to save a copy of it to your device’s local storage. Here’s how you can do it:
- Locate the file you want to save.
- Tap on the three dots (⋮) next to the file name.
- From the menu that appears, select "Save a Copy."
Once the file is saved to your device’s local storage, you will be able to access it even without an internet connection https://helpx.adobe.com/acrobat/mobile-app-faq.html
Let me know if you need any more help!