I can find no way to delete unwanted documents.
Deleting files is an operation done in the operating system (Windows, Mac, Linux,etc) not an operation done in LibreOffice or even Microsoft Office. Therefore please look for information on how to delete, copy, paste and move files using your operation system.
Typically you can open a “window” showing you folders and files and by right clicking on folders and file you can delete, copy, paste and move files. How this window is called depends on your operating system.
Does NOT work!
A document will still have an entry in the Recent Documents list even after it has been deleted from the file system.
You can clear the list from the menu option File/Recent Documents/Clear List.
In newer versions of LibreOffice there is a cross in the top right corner of the Document Icon when you hover over it from the start screen. Click on that to remove the entry for that document.
Richard
Does NOT work!