What kind of documents ? Text , PDF, *.ppx, ..... ? And with what programs ? MS Word, Open Office, Foxit PDF reader, Powerpoint (viewer), ....... ?
Sounds like your AV is slowing down the opening of files. Do you have multple AV programs running ? E.g. WinDefender & AVAST ? If you have e.g. AVAST AV you can disable the WinDefend Service.