it's been forever since I used iTunes for anything, let alone file transfer. I'm not even certain how it works anymore. For instance, does it only show local iPad folders for sharing, or do the iCloud folder show up?
At any rate, I would not continue to depend on it. It is largely a legacy method of transferig fliles, and Apple could abandon it altogether at any time.
That said, here are a few alternatives. The first two will work with local iPad folders. The other's will only work if you are using iCloud Storage.
I see you have PDF Expert. I use Documents, which is a super set of PDF expert. One of he options under Connections (in the left bar in the app) is Computer. It you chose that it will walk you through connecting to your computer through a browser; provided it is on the same wi-fi network. You can then use the computer to transfer files to/from Documents.
Many document type apps have this option.
You can also connect to your computer in the Files app. Tap on the three dot (...) menu at the top left of the Files menu bar. Chose Connect to Server. On my Mac all I have to do is go to the computer's wi-fi setting, find out what the IP address is, and use that. Then use your computer's username and password to log in. What ever files/folder you've set up to share on the computer and now available in Files on the iPad. I find the persistence of this connection unpredictable. You may have to re-connect occasionally. And since computer IP addresses on a local network can change, you may have to look it up again, now and then.
If you are using iCloud storage, you can access that on your computer. On a Mac, you just have to be signed in to your Apple account on the computer, and iCloud wills how up automatically in the Finder. In Windows you'll have to install iCloud support. Most apps either store their files in iCloud by default, or have the option to do so. PDF Expert is one that has both local and iCloud storage folder.
If you wan't files to be generally available on both your computer and iPad, this is the least hassle, though you may have to up your iCloud storage tier.
Finally, provided you are using iCloud storage on the iPad you can access your files by going to iCloud.com in your computer's browser. This is handy if you find you need to grab a file wile using someone else's computer. You can also check your mail, look at your photos, edit Notes, and use Apple's other productivity apps. Just be sure to log out when you are done.
If you have details on what exactly you are trying to do, I, or other's may have more specific suggestions on how you can manage your files.
