An earlier preview is not enough
You are preparing for a trip and need an invoice or another document in PDF format to hand. You opened it on your phone before, so you expect it to remain available without a signal. Check this beforehand: an earlier preview is no reliable test of whether the entire file is available.
If you use Google Drive on Android, prepare the specific file for offline access, then test the same steps you will need while travelling.
Prepare the correct document version
While you are online, find and open the original PDF. Compare its supplier and document number with the purchase you will need to discuss. Go through every page. If you also have a corrected document, clearly label the original and corrected versions. Check which account holds the file too: personal and business Drive accounts can contain similarly named files.
Google’s Android offline guide says to open the file’s More menu and choose Make available offline. Find prepared files in the app menu under Offline. Labels may differ with the interface language.
Guide to offline use on Android →
If you cannot find the option for that PDF or preparation does not finish, do not assume it will work later. Check your account and the app’s available options; test any alternative route to a local copy against your company’s document handling procedure first.
A disconnected test tells you more than an icon
Once the file is ready, switch off Wi-Fi and mobile data. You can use airplane mode, but check that Wi-Fi has not stayed on. Return to Google Drive and open the document from Offline.
Go through every page, not just the first preview. Zoom in on the details you will need to read. If the file will not open or part is missing, you have discovered the problem before leaving. Reconnect, prepare the same file for offline access in Google Drive itself, then repeat the test from Offline once preparation has finished.
Opening one file successfully does not check the whole folder. If you need both an invoice and an order confirmation during the trip, test each required document separately.
An example of preparing before departure
In a fictional situation, you need to explain two items to your accountant while travelling. Prepare the relevant PDFs, open both offline and check the document numbers and item legibility. You now know which documents are available on that particular phone.
This check does not establish that your accountant received the files. Offline access on your device and delivery to the recipient are separate checks. If you also need to send the documents, use the agreed route while online and verify the actual handover result.
After returning, or after an invoice correction, check that you still have the required version. A local copy should let you read the correct document without a signal, rather than create another unlabelled file whose origin you later cannot identify.