Respectful or polite equivalent of 誰でも. Common in announcements, invitations, and polite speech when referring to people without specifying who.
このイベントにはどなたでも参加できます。
Anyone can participate in this event.
ご質問はどなたでもご自由にどうぞ。
Anyone is welcome to ask questions.
Anyone can take part in this event.
初心者からベテランまで、どなたでも大歓迎です。
From beginners to veterans, everyone is welcome.
This library can be used by anyone.
どなたか means 'someone/anyone' in a question or request about a single unspecified person, whereas どなたでも means 'anyone at all, no matter who.'
Formed from どなた, a respectful interrogative for 'who,' plus でも, which gives an inclusive sense like 'even' or 'any.'