I have only used Airdrop with Photos images and those are placed in Photos on the receiving device. That works the same going from desktop to iPad/iPhone and vice versa.
My normal procedure for data files and folders is to move them to my iCloud account where they are available to my desktop, iPad, and iPhone.
When an iPad or iPhone app is directed to store files on iCloud they go into folders named for the creating application, for example Pages files will be in a folder labeled Pages and Keynote files will be in a folder names Keynote, etc. so I tend to follow the same pattern even though it is unnecessary on the desktop.
The Files app that is part of iOS 11 has iCloud file management functions similar to Finder on your desktop, but unlike Finder it does not identify files by extension and instead used the App's folder.
joemikeb • moderator