boxes with question marks

[rebar101]

after working on a document i've been working on for a while, several black boxes with question marks appeared and i can't undo.

[Dov Isaacs]

Exactly what do you mean by “working on a document?” Exactly what are you doing and with what version of Acrobat?

          - Dov

[philippanmei]

give us screenshot to understand more

thanks