Margin Adjustment

Unlike a physical sheet of paper, a PDF page is defined mathematically by five distinct boundary boxes.

• MediaBox: The physical medium (e.g., A4 paper size).
• CropBox: The visible region displayed or printed.
• BleedBox: Defines the region to which the contents of the page should be clipped when output in a production environment.
• TrimBox: The intended dimensions of the finished page after trimming.
• ArtBox: The extent of the page's meaningful content.

When you add margins to a PDF using this tool, we aren't just drawing white rectangles on the edges. Instead, we are mathematically expanding the MediaBox and CropBox coordinates.

If you want the content to stay the same size but have more whitespace around it, we translate (shift) the existing content stream and expand the bounding box dimensions.

If you want to scale the content down to fit within new, larger margins without changing the overall page size, we apply an Affine Transformation Matrix.

This matrix multiplies the coordinates of every path, image, and text block in the page's content stream, uniformly scaling them down and re-centering them on the canvas.