ENH: Add PDF/A XMP metadata support (#3314)

Closes #3313.

---------

Signed-off-by: Arya Nair <aryaajitnair@gmail.com>
Co-authored-by: Stefan <96178532+stefan6419846@users.noreply.github.com>

Author: Arya-A-Nair

pypdf/xmp.py

@@ -52,6 +52,9 @@
 # Schemas".
 PDFX_NAMESPACE = "http://ns.adobe.com/pdfx/1.3/"
 
+# PDF/A
+PDFAID_NAMESPACE = "http://www.aiim.org/pdfa/ns/id/"
+
 iso8601 = re.compile(
     """
         (?P<year>[0-9]{4})
@@ -363,6 +366,12 @@ def _get_text(self, element: XmlElement) -> str:
     """An identifier for a specific incarnation of a document, updated each
     time a file is saved."""
 
+    pdfaid_part = property(_getter_single(PDFAID_NAMESPACE, "part"))
+    """The part of the PDF/A standard that the document conforms to (e.g., 1, 2, 3)."""
+
+    pdfaid_conformance = property(_getter_single(PDFAID_NAMESPACE, "conformance"))
+    """The conformance level within the PDF/A standard (e.g., 'A', 'B', 'U')."""
+
     @property
     def custom_properties(self) -> Dict[Any, Any]:
         """

tests/test_xmp.py

@@ -272,3 +272,25 @@ class Tst:  # to replace pdf
 
     assert xmp_info is not None
     f(xmp_info)
+
+
+@pytest.mark.samples
+def test_pdfa_xmp_metadata_with_values():
+    """Test PDF/A XMP metadata extraction from a file with PDF/A metadata."""
+    reader = PdfReader(SAMPLE_ROOT / "021-pdfa" / "crazyones-pdfa.pdf")
+    xmp = reader.xmp_metadata
+
+    assert xmp is not None
+    assert xmp.pdfaid_part == "1"
+    assert xmp.pdfaid_conformance == "B"
+
+
+@pytest.mark.samples
+def test_pdfa_xmp_metadata_without_values():
+    """Test PDF/A XMP metadata extraction from a file without PDF/A metadata."""
+    reader = PdfReader(SAMPLE_ROOT / "020-xmp" / "output_with_metadata_pymupdf.pdf")
+    xmp = reader.xmp_metadata
+
+    assert xmp is not None
+    assert xmp.pdfaid_part is None
+    assert xmp.pdfaid_conformance is None