feat: Add page metadata on PDFMinerLoader (#12277)

- **Description:** #12273 's suggestion PR
Like other PDFLoader, loading pdf per each page and giving page
metadata.
  - **Issue:** #12273 
  - **Twitter handle:** @blue0_0hope

---------

Co-authored-by: Eugene Yurtsev <eyurtsev@gmail.com>

libs/langchain/langchain/document_loaders/parsers/pdf.py

@@ -128,18 +128,36 @@ class PyPDFParser(BaseBlobParser):
 class PDFMinerParser(BaseBlobParser):
     """Parse `PDF` using `PDFMiner`."""
 
-    def __init__(self, extract_images: bool = False):
+    def __init__(self, extract_images: bool = False, *, concatenate_pages: bool = True):
+        """Initialize a parser based on PDFMiner.
+
+        Args:
+            extract_images: Whether to extract images from PDF.
+            concatenate_pages: If True, concatenate all PDF pages into one a single
+                               document. Otherwise, return one document per page.
+        """
         self.extract_images = extract_images
+        self.concatenate_pages = concatenate_pages
 
     def lazy_parse(self, blob: Blob) -> Iterator[Document]:
         """Lazily parse the blob."""
+
         if not self.extract_images:
             from pdfminer.high_level import extract_text
 
             with blob.as_bytes_io() as pdf_file_obj:
-                text = extract_text(pdf_file_obj)
-                metadata = {"source": blob.source}
-                yield Document(page_content=text, metadata=metadata)
+                if self.concatenate_pages:
+                    text = extract_text(pdf_file_obj)
+                    metadata = {"source": blob.source}
+                    yield Document(page_content=text, metadata=metadata)
+                else:
+                    from pdfminer.pdfpage import PDFPage
+
+                    pages = PDFPage.get_pages(pdf_file_obj)
+                    for i, _ in enumerate(pages):
+                        text = extract_text(pdf_file_obj, page_numbers=[i])
+                        metadata = {"source": blob.source, "page": str(i)}
+                        yield Document(page_content=text, metadata=metadata)
         else:
             import io
 

libs/langchain/langchain/document_loaders/pdf.py

@@ -251,8 +251,15 @@ class PDFMinerLoader(BasePDFLoader):
         *,
         headers: Optional[Dict] = None,
         extract_images: bool = False,
+        concatenate_pages: bool = True,
     ) -> None:
-        """Initialize with file path."""
+        """Initialize with file path.
+
+        Args:
+            extract_images: Whether to extract images from PDF.
+            concatenate_pages: If True, concatenate all PDF pages into one a single
+                               document. Otherwise, return one document per page.
+        """
         try:
             from pdfminer.high_level import extract_text  # noqa:F401
         except ImportError:
@@ -262,7 +269,9 @@ class PDFMinerLoader(BasePDFLoader):
             )
 
         super().__init__(file_path, headers=headers)
-        self.parser = PDFMinerParser(extract_images=extract_images)
+        self.parser = PDFMinerParser(
+            extract_images=extract_images, concatenate_pages=concatenate_pages
+        )
 
     def load(self) -> List[Document]:
         """Eagerly load the content."""

libs/langchain/tests/integration_tests/document_loaders/test_pdf.py

@@ -56,6 +56,19 @@ def test_pdfminer_loader() -> None:
     docs = loader.load()
     assert len(docs) == 1
 
+    # Verify that concatenating pages parameter works
+    file_path = Path(__file__).parent.parent / "examples/hello.pdf"
+    loader = PDFMinerLoader(str(file_path), concatenate_pages=True)
+    docs = loader.load()
+
+    assert len(docs) == 1
+
+    file_path = Path(__file__).parent.parent / "examples/layout-parser-paper.pdf"
+    loader = PDFMinerLoader(str(file_path), concatenate_pages=False)
+
+    docs = loader.load()
+    assert len(docs) == 16
+
 
 def test_pdfminer_pdf_as_html_loader() -> None:
     """Test PDFMinerPDFasHTMLLoader."""