i just now removed all the recent documents by error, how can recent documents be restored
Hello rosemary
if you mean by removed all the recent documents that they do not appear any longer in overview pane (preview list of recently used document) when LibreOffice Starter has been started (which is the same thing as looking into File -> Recent Documents then the answer is: No restore possible. The name (!!!) of the files (not the files itself) have been removed from History in the User Profile (to be technically precise: from file registrymodifications.xcu). The only way to get this information back into History is to open the files (of course you need to know, where they are stored on your filesystem) one after the other.
If you mean that you deleted the files itself, then you may have good luck and they are still in the “trash” and can be restored from there or, depending on your LibreOffice, you may be lucky and you’ll be able to restore from your user profile’s backup directory. Since you did not tell us about you operating system, I cannot tell you, were to find the backup directory. Please consult https://wiki.documentfoundation.org/UserProfile.