fix: get accurate pdf page size (#1980)

Handles edge cases with PDF media boxes and crop boxes, deals with
certain documents that had been uploaded with weird combos of sizings.

packages/lib/server-only/pdf/get-page-size.ts

@@ -0,0 +1,18 @@
+import type { PDFPage } from 'pdf-lib';
+
+/**
+ * Gets the effective page size for PDF operations.
+ *
+ * Uses CropBox by default to handle rare cases where MediaBox is larger than CropBox.
+ * Falls back to MediaBox when it's smaller than CropBox, following typical PDF reader behavior.
+ */
+export const getPageSize = (page: PDFPage) => {
+  const cropBox = page.getCropBox();
+  const mediaBox = page.getMediaBox();
+
+  if (mediaBox.width < cropBox.width || mediaBox.height < cropBox.height) {
+    return mediaBox;
+  }
+
+  return cropBox;
+};