Adding a .Root attribute in PdfWriter to allow setting its MediaBox or Resources fields

Author: Cimon Lucas (LCM)

pdfrw/pdfwriter.py

@@ -262,6 +262,7 @@ def __init__(self, fname=None, version='1.3', compress=False, **kwargs):
                                      "on PdfWriter instance" % name)
                 setattr(self, name, value)
 
+        self.Root = None
         self.pagearray = PdfArray()
         self.killobj = {}
 
@@ -310,16 +311,14 @@ def _get_trailer(self):
             self.make_canonical()
 
         # Create the basic object structure of the PDF file
-        trailer = PdfDict(
-            Root=IndirectPdfDict(
-                Type=PdfName.Catalog,
-                Pages=IndirectPdfDict(
-                    Type=PdfName.Pages,
-                    Count=PdfObject(len(self.pagearray)),
-                    Kids=self.pagearray
-                )
-            )
+        catalog_root = self.Root or IndirectPdfDict()
+        catalog_root.Type = PdfName.Catalog
+        catalog_root.Pages = IndirectPdfDict(
+            Type=PdfName.Pages,
+            Count=PdfObject(len(self.pagearray)),
+            Kids=self.pagearray
         )
+        trailer = PdfDict(Root=catalog_root)
         # Make all the pages point back to the page dictionary and
         # ensure they are indirect references
         pagedict = trailer.Root.Pages