10. A non-transitory computer-readable medium storing a program that causes a computer to execute document processing, the document processing comprising: acquiring document data containing plural pieces of page image data corresponding to respective pages of a plurality of documents, each document being formed by stacking and half-folding sheets; a first detection step of detecting, based on characteristics of the plural pieces of page image data, pieces of page image data corresponding to pages to be printed on a same side of a same sheet in the documents, from the plural pieces of page image data contained in the document data; specifying, based on positions of the detected pieces of page image data in the document data, pieces of page image data corresponding to respective pages of each document, from the plural pieces of page image data contained in the document data; outputting data, which is based on pieces of page image data corresponding to respective pages of at least one of the documents, based on a result of the specifying a second detection step of detecting page image data having an image drawn in a first area corresponding to a first end; and a third detection step of detecting page image data having an image drawn in a second area corresponding to a second end opposed to the first end, wherein the first detection step detects the pieces of page image data corresponding to the pages to be printed on the same side of the same sheet in the documents, based on a result of the second detection step and a result of the third detection step.
10. A non-transitory computer-readable medium storing a program that causes a computer to execute document processing, the document processing comprising: acquiring document data containing plural pieces of page image data corresponding to respective pages of a plurality of documents, each document being formed by stacking and half-folding sheets; a first detection step of detecting, based on characteristics of the plural pieces of page image data, pieces of page image data corresponding to pages to be printed on a same side of a same sheet in the documents, from the plural pieces of page image data contained in the document data; specifying, based on positions of the detected pieces of page image data in the document data, pieces of page image data corresponding to respective pages of each document, from the plural pieces of page image data contained in the document data; outputting data, which is based on pieces of page image data corresponding to respective pages of at least one of the documents, based on a result of the specifying a second detection step of detecting page image data having an image drawn in a first area corresponding to a first end; and a third detection step of detecting page image data having an image drawn in a second area corresponding to a second end opposed to the first end, wherein the first detection step detects the pieces of page image data corresponding to the pages to be printed on the same side of the same sheet in the documents, based on a result of the second detection step and a result of the third detection step. 11. The non-transitory computer-readable medium according to claim 10 , wherein the document data is configured so that the plural pieces of page image data corresponding to the respective pages of the plurality of documents can be read out in a predetermined order, the document processing further comprises determining as to whether or not a rank of the page image data detected in the second detection step and a rank of the page image data detected in the third detection step have a predetermined relationship therebetween, and when it is determined that the rank of the page image data detected in the second detection step and the rank of the page image data detected in the third detection step have the predetermined relationship, the first detection step detects that the page image data detected in the second detection step and the page image data detected in the third detection step are the pieces of page image data corresponding to the pages to be printed on the same side of the same sheet in the documents.