Export Graphic to pdf

While exporting graphic to pdf - if the previous pdf is already open in the background and we want to replace/save the new pdf with the same name as the previous one...its generating a new pdf file with a new name...for example I tried to give the first pdf name as "aris-test1.pdf" and opened in the background, made some changes to the graphic and tried to export it to pdf with the same name, but the system generated a new pdf file with the name "aris-test10.pdf'....this is repeating and if the follow the same process, the next file that is automatically generated has a name of "aris-test100.pdf"....