1. A document management system capable of managing a plurality of documents in which attribute names and attribute values corresponding to the attribute names are set as attributes, the document management system comprising: an attribute display unit configured to display the attribute names and the attribute values set for a document selected from the plurality of documents; a selection unit configured to select at least one attribute value from the attribute values displayed by the attribute display unit; a search screen display unit configured to, when an instruction to display a search screen is issued, display the search screen; and a setting unit configured to set a search conditional expression of an attribute search in the search screen; wherein if the instruction to display the search screen is issued in a state where the at least one attribute value is selected by the selection unit, the search screen display unit displays the search screen in which the at least one attribute value selected by the selection unit is set for the search conditional expression by the setting unit.