also try concatenating local pdf files with labels

poetry.lock

@@ -309,6 +309,14 @@ optional = false
 python-versions = ">=3.5"
 version = "2.6.1"
 
+[[package]]
+category = "main"
+description = "PDF toolkit"
+name = "pypdf2"
+optional = false
+python-versions = "*"
+version = "1.26.0"
+
 [[package]]
 category = "main"
 description = "Pure Python module to hyphenate text"
@@ -412,7 +420,7 @@ python-versions = "*"
 version = "0.5.1"
 
 [metadata]
-content-hash = "f551392acf27b79f04c5fab68df548257f3a538875f9b4bf501e4633a3761860"
+content-hash = "56be8de37de7b07fbe5ca98c9ceea5ca22dbd2ddb2053e252bc41baf6293c373"
 python-versions = "^3.8"
 
 [metadata.files]
@@ -561,6 +569,9 @@ pygments = [
     {file = "Pygments-2.6.1-py3-none-any.whl", hash = "sha256:ff7a40b4860b727ab48fad6360eb351cc1b33cbf9b15a0f689ca5353e9463324"},
     {file = "Pygments-2.6.1.tar.gz", hash = "sha256:647344a061c249a3b74e230c739f434d7ea4d8b1d5f3721bc0f3558049b38f44"},
 ]
+pypdf2 = [
+    {file = "PyPDF2-1.26.0.tar.gz", hash = "sha256:e28f902f2f0a1603ea95ebe21dff311ef09be3d0f0ef29a3e44a932729564385"},
+]
 pyphen = [
     {file = "Pyphen-0.9.5-py2.py3-none-any.whl", hash = "sha256:e172faf10992c8c9d369bdc83e36dbcf1121f4ed0d881f1a0b521935aee583b5"},
     {file = "Pyphen-0.9.5.tar.gz", hash = "sha256:3b633a50873156d777e1f1075ba4d8e96a6ad0a3ca42aa3ea9a6259f93f18921"},

pyproject.toml

@@ -9,6 +9,7 @@ python = "^3.8"
 django = "^3.0.4"
 django-model-utils = "^4.0.0"
 weasyprint = "^51"
+pypdf2 = "^1.26.0"
 
 [tool.poetry.dev-dependencies]
 ipython = "^7.13.0"

sdbs_pile/pile/views.py

@@ -1,8 +1,10 @@
 # Create your views here.
 import io
+import logging
 from operator import itemgetter
 
 import weasyprint
+from PyPDF2 import PdfFileWriter, PdfFileReader
 from django.contrib.syndication.views import Feed
 from django.core.exceptions import ObjectDoesNotExist
 from django.http import Http404, FileResponse
@@ -106,11 +108,27 @@ class DocumentWithLabel(BasePileViewMixin):
 
         label_html = render_to_string("label.html", {'document': document})
 
-        stream = io.BytesIO()
-        weasyprint.HTML(base_url=request.build_absolute_uri(), string=label_html).write_pdf(stream)
-        stream.seek(0)
+        label_stream = io.BytesIO()
+        weasyprint.HTML(base_url=request.build_absolute_uri(), string=label_html).write_pdf(label_stream)
+        label_stream.seek(0)
 
-        return FileResponse(stream,
+        final_stream = label_stream
+
+        if document.file:
+            try:
+                with open(document.file.path, 'rb') as document_fp:
+                    writer = PdfFileWriter()
+                    for reader in map(PdfFileReader, (label_stream, document_fp)):
+                        for n in range(reader.getNumPages()):
+                            writer.addPage(reader.getPage(n))
+                    final_stream = io.BytesIO()
+                    writer.write(final_stream)
+                    final_stream.seek(0)
+            except Exception as exc:
+                logging.exception(exc)
+                final_stream = label_stream
+
+        return FileResponse(final_stream,
                             filename=f"pile_{document.id}__{slugify(document.title)}.pdf",
                             content_type="application/pdf")