17. A document processing program stored on a non-transitory computer-readable medium which operates in a multi-task environment in which a plurality of application programs can be executed, causing a computer to execute: a first display function which causes a display unit to display a first screen of a first application program and a second screen of a second application program; a switching detecting function which detects switching from the first application program to the second application program; a character string extracting function which generates, in response to detection of the switching by the switching detecting function, 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 may be used in the second application program; and a second display function which causes the display unit to display the list including the character strings on the second screen, and receives a selection by a user of at least one of the character strings from the list for use by the second application program, and causes the at least one of the character strings from the list to be input to a predetermined region of the second application program.
17. A document processing program stored on a non-transitory computer-readable medium which operates in a multi-task environment in which a plurality of application programs can be executed, causing a computer to execute: a first display function which causes a display unit to display a first screen of a first application program and a second screen of a second application program; a switching detecting function which detects switching from the first application program to the second application program; a character string extracting function which generates, in response to detection of the switching by the switching detecting function, 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 may be used in the second application program; and a second display function which causes the display unit to display the list including the character strings on the second screen, and receives a selection by a user of at least one of the character strings from the list for use by the second application program, and causes the at least one of the character strings from the list to be input to a predetermined region of the second application program. 18. The document processing program according to claim 17 , wherein the document processing program is provided as a part of functions of the first application program.