Currently, you could import a single PDF into Acrobat on iPhone and iPad. The steps are as followings,
1. Installed Dropbox and Acrobat applications on your device,
2. Run Dropbox application and sign in to your Dropbox account
3. Run Acrobat application
4. In Dropbox application, open a PDF
5. At upper right hand corner, tap "。。。"
6. Tap "Export" in the drop-down menu
7. Tap "Open In" in the popover menu
8. Tap "Copy to Adobe Acrobat" in popover menu
Now, the PDF should be opened and copied to Acrobat "Local".
Hope this help.