code: public void setHasFacingPages() {
          if(this.mode == MODE_SINGLE) {
              this.mode = MODE_MULTIPLE;
              this.headerLeft = new RtfHeaderFooter(this.document, this.headerAll, RtfHeaderFooter.DISPLAY_LEFT_PAGES);
              this.headerLeft.setType(this.type);
              this.headerRight = new RtfHeaderFooter(this.document, this.headerAll, RtfHeaderFooter.DISPLAY_RIGHT_PAGES);
              this.headerRight.setType(this.type);
              this.headerAll = null;
          } else if(this.mode == MODE_MULTIPLE) {
              if(this.headerLeft == null && this.headerAll != null) {
                  this.headerLeft = new RtfHeaderFooter(this.document, this.headerAll, RtfHeaderFooter.DISPLAY_LEFT_PAGES);
                  this.headerLeft.setType(this.type);
              }
              if(this.headerRight == null && this.headerAll != null) {
                  this.headerRight = new RtfHeaderFooter(this.document, this.headerAll, RtfHeaderFooter.DISPLAY_RIGHT_PAGES);
                  this.headerRight.setType(this.type);
              }
              this.headerAll = null;
          }
      }
docs: Set that this RtfHeaderFooterGroup should have facing pages. If only
  a header / footer for all pages exists, then it will be copied to the left
  and right pages as well.