Open Google Docs in Google Chrome
Make sure you are signed in to your Google account
Install the Google Docs Offline extension if prompted
Open Google Drive settings
Turn on Offline
Wait for files to finish syncing
Open the Google Doc you want available offline
Keep the document open until it is fully saved for offline use
To access it later, open Google Docs while offline and select the document
On mobile, open the Google Docs app
Open the document
Tap the three dots menu
Turn on Available offline