ENH: Add PdfWriter.open_destination property

PyPDF2/_writer.py

@@ -411,6 +411,54 @@ def insertBlankPage(
         deprecate_with_replacement("insertBlankPage", "insert_blank_page")
         return self.insert_blank_page(width, height, index)
 
+    @property
+    def open_destination(
+        self,
+    ) -> Union[None, Destination, TextStringObject, ByteStringObject]:
+        """
+        Property to access the opening destination ("/OpenAction" entry in the
+        PDF catalog).
+        it returns `None` if the entry does not exist is not set.
+
+        :param destination:.
+        the property can be set to a Destination, a Page or an string(NamedDest) or
+            None (to remove "/OpenAction")
+
+        (value stored in "/OpenAction" entry in the Pdf Catalog)
+        """
+        if "/OpenAction" not in self._root_object:
+            return None
+        oa = self._root_object["/OpenAction"]
+        if isinstance(oa, (str, bytes)):
+            return create_string_object(str(oa))
+        elif isinstance(oa, ArrayObject):
+            try:
+                page, typ = oa[0:2]  # type: ignore
+                array = oa[2:]
+                return Destination("OpenAction", page, typ, *array)  # type: ignore
+            except Exception:
+                raise Exception(f"Invalid Destination {oa}")
+        else:
+            return None
+
+    @open_destination.setter
+    def open_destination(self, dest: Union[None, str, Destination, PageObject]) -> None:
+        if dest is None:
+            try:
+                del self._root_object["/OpenAction"]
+            except KeyError:
+                pass
+        elif isinstance(dest, str):
+            self._root_object[NameObject("/OpenAction")] = TextStringObject(dest)
+        elif isinstance(dest, Destination):
+            self._root_object[NameObject("/OpenAction")] = dest.dest_array
+        elif isinstance(dest, PageObject):
+            self._root_object[NameObject("/OpenAction")] = Destination(
+                "Opening",
+                dest.indirect_ref if dest.indirect_ref is not None else NullObject(),
+                TextStringObject("/Fit"),
+            ).dest_array
+
     def add_js(self, javascript: str) -> None:
         """
         Add Javascript which will launch upon opening this PDF.

tests/test_writer.py

@@ -9,6 +9,7 @@
 from PyPDF2.generic import (
     IndirectObject,
     NameObject,
+    NumberObject,
     RectangleObject,
     StreamObject,
     TextStringObject,
@@ -813,3 +814,44 @@ def test_write_empty_stream():
     with pytest.raises(ValueError) as exc:
         writer.write("")
     assert exc.value.args[0] == "Output(stream=) is empty."
+
+
+def test_startup_dest():
+    pdf_file_writer = PdfWriter()
+    pdf_file_writer.append_pages_from_reader(PdfReader(RESOURCE_ROOT / "issue-604.pdf"))
+
+    assert pdf_file_writer.open_destination is None
+    pdf_file_writer.open_destination = pdf_file_writer.pages[9]
+    # checked also using Acrobrat to verify the good page is opened
+    op = pdf_file_writer._root_object["/OpenAction"]
+    assert op[0] == pdf_file_writer.pages[9].indirect_ref
+    assert op[1] == "/Fit"
+    op = pdf_file_writer.open_destination
+    assert op.raw_get("/Page") == pdf_file_writer.pages[9].indirect_ref
+    assert op["/Type"] == "/Fit"
+    pdf_file_writer.open_destination = op
+    assert pdf_file_writer.open_destination == op
+
+    # irrelevant, just for coverage
+    pdf_file_writer._root_object[NameObject("/OpenAction")][0] = NumberObject(0)
+    pdf_file_writer.open_destination
+    with pytest.raises(Exception) as exc:
+        del pdf_file_writer._root_object[NameObject("/OpenAction")][0]
+        pdf_file_writer.open_destination
+    assert "Invalid Destination" in str(exc.value)
+
+    pdf_file_writer.open_destination = "Test"
+    # checked also using Acrobrat to verify open_destination
+    op = pdf_file_writer._root_object["/OpenAction"]
+    assert isinstance(op, TextStringObject)
+    assert op == "Test"
+    op = pdf_file_writer.open_destination
+    assert isinstance(op, TextStringObject)
+    assert op == "Test"
+
+    # irrelevant, this is just for coverage
+    pdf_file_writer._root_object[NameObject("/OpenAction")] = NumberObject(0)
+    assert pdf_file_writer.open_destination is None
+    pdf_file_writer.open_destination = None
+    assert "/OpenAction" not in pdf_file_writer._root_object
+    pdf_file_writer.open_destination = None