1. A method of editing a document, the method comprising: accessing, by a streaming execution unit, a second terminal of a second user via a first terminal of a first user; visualizing, by the streaming execution unit, a second document file, which is selected by the first user in the first terminal and is a document file of a predetermined sharing folder of the second terminal, on a display unit of the first terminal in a streaming manner; and extracting, by an edited document generation unit, an area of interest from the second document file visualized on the display unit of the first terminal in a streaming manner in response to a manipulation of the first user, and generating, by the edited document generation unit, an edited document; wherein the document file is a portable document format (PDF) file, wherein generating the edited document comprises: generating an editing space file that is an initial file used to generate the edited document; generating a clipping mask used to extract the area of interest; extracting the area of interest corresponding to the clipping mask from the second document file; copying the extracted area of interest to the editing space file, and processing the edited document; determining an entity attribute of the extracted area of interest; and determining a copy region, which belongs to the extracted area of interest and will be copied to the editing space file, based on the security of the extracted area of interest and the entity attribute; wherein determining the copy region comprises: deleting data corresponding to a part that belongs to the extracted area of interest and that corresponds to the confidential region, thereby determining the copy region; and performing effect processing set by a user or predetermined effect processing on the region deleted by a data deletion unit; wherein deleting the data comprises: computing a minimum square-shaped bounding box including a clipping line, that is, a boundary line of the clipping mask; converting a page coordinate system, that is, a coordinate system based on a page of the second document file, into an image coordinate system, that is, a coordinate system based on an image present in the second document file; converting the bounding box into the image coordinate system; deleting data, corresponding to the confidential region included in a conversion bounding box and a part placed outside the conversion bounding box, based on the conversion bounding box converted into the image coordinate system; and performing the effect processing comprises performing shading processing on the deleted region in order for a user not to view the part corresponding to the confidential region.