I'm trying to upload the older mileage in PDF file on QuickBooks but don't know how

Good morning, lewis-idhome-ca.

Welcome to the QuickBooks Community! Although QuickBooks Online doesn't have the option to import mileage, I can show you how to manually enter mileage by following the steps below: 

1. Sign in to QuickBooks Online in a web browser.
2. Go to "Apps" and select "Mileage".
3. Select "Add trip".
4. Add the trip date, starting and ending locations, distance, and the purpose.
5. Chose the vehicle you used.
6. Hit "Save".

Here's an article that explains this process in more detail. 

If you have any other questions, feel free to reach back out here.