Hi there, when the document folder located in the C drive disappeared after the Windows 10 update, you should go to the basic location to have a look first. You can head to the Recycle Bin or File Explorer to search for the files and see if they appear.
If the document folder was missing, you're suggested to restore your files via File History. Here I am gonna show you how to do:
Step 1: Press the Win + S keys and type in File History to run the File History on your PC.
Step 2: Click Restore your files with File History.
Step 3: Use the left and right arrows to browse through different versions of your folders and files. Or you can search your files with file name or format in the search box.
Step 4: Select the file you intend to restore and click the Restore button and the files will be saved to the original location. If you want to restore them to a new location, right-click the Restore button and select Restore To, and then determine the new location.
Alternatively, you can go back to the point before the Windows update. Follow the steps below:
Step 1: Go the Settings and select Update & Security.
Step 2: Click Recovery and tap Restart under the Advanced startup.
Step 3: Choose Troubleshoot in the Advanced startup screen.
Step 4: Select Advanced options then click System Restore.
Hope this answer helps you solve your problem!