How you retrieve my lost documents

From an iCloud Backup? Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

Note that it involves erasing and restoring the entire device and that it will replace the current contents of the device with the contents from the time of the backup.

A document synced to iCloud Drive? Log into www.icloud.com and click Account Settings near the top middle of that screen and then go to the Advanced section of the next screen and click Restore Files.