mobile DropBox : how to make sure docs downloaded locally when sync happen and can be readable even Cell goes offline

presently my dropbox  account configured in my PC + Andriod Phone.
usually I add docs from my PC and read from mobile when I felt like to read.

Issue is -Docs those uploaded from my PC, am able to viewe and open from my mobile only when it is online(connected to Net.
When Cell goes offline and tried to open the same, am getting offline error.

I wish the docs to be downloaded locally in andriod cell when sync happen with my PC  when both are online and should be able to read even my cell goes offline mode.

please advice how to achieve ?