Split Adobe PDF pages down the middle or with an offset, and exclude variable number of pages from the front of doc.

splitpages.js

cut = function(offset, start)
{
    start = start || 1;
    offset = offset || 0;
    // create a new document
    app.beginPriv();
    var newDoc = app.newDoc();
    app.endPriv();

    // get the filename of our current file

    var i = 0;
    while (i < start - 1) {
        newDoc.insertPages( {
            nPage: newDoc.numPages - 1,
            cPath: this.path,
            nStart: i
        });
        i++;
    }

    while (i < this.numPages)
    {
        newDoc.insertPages( {
            nPage: newDoc.numPages-1,
            cPath: this.path,
            nStart: i
        });
        newDoc.insertPages( {
            nPage: newDoc.numPages-1,
            cPath: this.path,
            nStart: i
        });
        // we did this twice so that we can then split each copy of the page into a left
        // and right half. 
        i++;
    }

    if (newDoc.numPages > 1)
    {
        newDoc.deletePages(0);	// this gets rid of the page that was created with the newDoc call.
    }

    // at this point we have a documnent with every page from the source document
    // copied twice

    for (i=start - 1; i<newDoc.numPages; i++)
    {
        // determine the crop box of the page
        var cropRect = newDoc.getPageBox("Crop", i);
        var halfWidth = (cropRect[2]-cropRect[0])/2;

        var cropLeft = new Array();
        cropLeft[0] = cropRect[0];
        cropLeft[1] = cropRect[1];
        cropLeft[2] = cropRect[0] + halfWidth + offset;
        cropLeft[3] = cropRect[3];

        var cropRight = new Array();
        cropRight[0] = cropRect[2] - halfWidth + offset;
        cropRight[1] = cropRect[1];
        cropRight[2] = cropRect[2];
        cropRight[3] = cropRect[3];

        if ((start-1) % 2 == 0) {
            if (i%2 == 0) {
                newDoc.setPageBoxes( {
                    cBox: "Crop",
                    nStart: i,
                    rBox: cropLeft
                });
            } else {
                newDoc.setPageBoxes( {
                    cBox: "Crop",
                    nStart: i,
                    rBox: cropRight
                });
            }
        } else {
            if (i%2 == 1) {
                newDoc.setPageBoxes( {
                    cBox: "Crop",
                    nStart: i,
                    rBox: cropLeft
                });
            } else {
                newDoc.setPageBoxes( {
                    cBox: "Crop",
                    nStart: i,
                    rBox: cropRight
                });
            }
        }
    }
}