Vector N-Up Imposition in PDFs Using Form XObjects and Affine Matrices

The article explains how print workflows place several logical pages onto one physical sheet, such as 2-up or 4-up layouts, without rasterizing them. Rasterizing degrades vector text and inflates file size, so the author proposes wrapping each source page as a PDF Form XObject. Each page is then positioned into a grid cell using a 2D affine transformation matrix applied through the cm operator and invoked with Do. The piece outlines the page dictionary structure and why separate Form XObjects avoid resource name collisions and coordinate conflicts. It also gives formulas for cell dimensions and origins on a sheet with margins and gutters, and promises a JavaScript implementation using pdf-lib.