You can use a USB flash disk with an otg interface to directly insert it into the phone. If there is no such USB flash disk, you can take the following steps to solve the problem:
Prepare an otg line and connect it to the USB flash drive;
Connect the otg connector to the mobile phone;
If there is no display in the mobile interface and document management, it must be manually set;
Turn on the otg function in the "Settings" of the phone;
In the regular interface, slide the screen and click the "More" font under "About Mobile Phone";
Check whether the otg connection is open, and click Open;
At this time, the interface displays the words "connected successfully";
After the USB flash drive is successfully connected, you can enter the document operation.