13. The document processing apparatus according to claim 1 , further comprising: a filter storing unit configured to store an object filter which detects a character string representing a position of an external object file from the document file, wherein the list includes an item associated with the one or more character strings detected by the character string extracting unit by using the object filter.
1. A document processing apparatus having a processor coupled to a memory device, which operates in a multi-task environment in which a plurality of application programs can be executed, comprising: a display unit configured to display a first screen displayed by a first application program and a second screen displayed by a second application program; a switching detecting unit configured to detect switching from the first application program to the second application program; a character string extracting unit configured to generate, in response to detection of the switching by the switching detecting unit, a list including character strings extracted from a document file having a content displayed on the first screen by using a filter serving as a rule to detect one or more character strings which can be used in the second application program; and a display control unit configured to cause the display unit to display the list including the character strings on the second screen, and configured to receive a selection by a user of at least one of the character strings from the list for use by the second application program, and configured to cause the at least one of the character strings from the list to be input to a predetermined region of the second application program.