Hi brixtonboy, one thing you have to take into consideration is how your hard drive was originally formatted. If your hard drive was formatted on a Windows PC, there’s a good chance it may have been formatted to NTFS.
Unfortunately the iPad Pro is unable to read that particular format. The iPad needs the hard drive to be formatted in a format that it can read, such as ExFAT. You may be lucky, but you won’t know until you try. One other thing you’ll probably need is some form of adaptor to convert the iPad’s usbc connector to the hard drives usba connector, unless the drive is usbc.
If your data is on an NTFS drive, then your only way to see it on your iPad Pro would be to transfer it to another drive that has been formatted to ExFAT using a PC (or perhaps a MAC).
The other thing to take into consideration is whether your drive is a conventional disc drive or an SSD (Solid State Drive), as most, if not all, SSD drives should not require external power, however some conventional drives MAY require a separate power unit.
Have a look on YouTube as there are some very good videos on using hard drives with the iPad Pro, and how to best use the ‘Files’ app to work with your files.