I have a user that when he tries to open office documents on a network volume or usb they only open in ‘read-only’. If he copies the file to his desktop and opens it everything is fine. He is on macOS 10.15.2 with the latest version of Office 219. This issue seems to have just started after replacing his hard drive with an SSD, although I don’t think the two are related. Has anyone else seen this odd behavior?
What file system on the USB drive? I had a kid buy one and just start using it. I think originally it was FAT, he reformatted and it worked (MacOS extended) right away. Our problem was from writing Xcode C++ files to his thumbdrive.
As to the network share, check that they're in the correct group and/or have read write permissions to that drive.
If no one else is having the same problems, its permissions/hardware.