第二个图像是正确的。裁剪框定义了页面画布上的框，查看器将显示该框。如果要保留可见的页面尺寸，请保持裁剪框的原样，并用白色填充除内部矩形外的所有裁剪框。
e、 g.像这样：

PDDocument document = ... the document to manipulate ...;
PDRectangle box = ... the rectangle to remain visible ...;

for (PDPage page : document.getPages()) {
    PDRectangle cropBox = page.getCropBox();
    try (PDPageContentStream canvas = new PDPageContentStream(document, page, AppendMode.APPEND, false, true)) {
        canvas.setNonStrokingColor(1);
        canvas.addRect(cropBox.getLowerLeftX(), cropBox.getLowerLeftY(), cropBox.getWidth(), cropBox.getHeight());
        canvas.addRect(box.getLowerLeftX(), box.getLowerLeftY(), box.getWidth(), box.getHeight());
        canvas.fillEvenOdd();
    }
}

（3）含量试验 testTrimCengage1 )
在你的评论中
你能把修剪过的那块放在书页中间吗？
是的，通过相应地调整裁剪框：

for (PDPage page : document.getPages()) {
    PDRectangle cropBox = page.getCropBox();
    cropBox = centerBoxAroundBox(box, cropBox.getWidth(), cropBox.getHeight());
    try (PDPageContentStream canvas = new PDPageContentStream(document, page, AppendMode.APPEND, false, true)) {
        canvas.setNonStrokingColor(1);
        canvas.addRect(cropBox.getLowerLeftX(), cropBox.getLowerLeftY(), cropBox.getWidth(), cropBox.getHeight());
        canvas.addRect(box.getLowerLeftX(), box.getLowerLeftY(), box.getWidth(), box.getHeight());
        canvas.fillEvenOdd();
    }
    page.setMediaBox(cropBox);
    page.setCropBox(cropBox);
}

（3）含量试验 testTrimAndCenterCengage1 )
使用此助手方法：

PDRectangle centerBoxAroundBox(PDRectangle box, float width, float height) {
    float horitontalMargins = (width - box.getWidth()) / 2;
    float verticalMargins = (height - box.getHeight()) / 2;
    return new PDRectangle(box.getLowerLeftX() - horitontalMargins, box.getLowerLeftY() - verticalMargins, width, height);
}

（三）内容辅助方法 centerBoxAroundBox )