diff --git a/doctor/tests.py b/doctor/tests.py
index ddca107..2dd4bc2 100644
--- a/doctor/tests.py
+++ b/doctor/tests.py
@@ -435,6 +435,33 @@ def test_get_document_number(self):
             self.assertEqual(doc_num, document_number)
 
 
+class TestDocumentNumberExtraction(unittest.TestCase):
+    def test_get_document_number_invalid_form(self):
+        """Test that we get a proper response when form validation fails"""
+        # Test with empty request
+        response = requests.post(
+            "http://doctor:5050/utils/document-number/pdf/",
+        )
+        self.assertEqual(response.status_code, 400, msg="Wrong status code")
+        self.assertIn(
+            "File is missing",
+            response.text,
+            msg="Wrong validation error message",
+        )
+
+        # Test with non-PDF file
+        with NamedTemporaryFile(suffix=".txt") as tmp:
+            tmp.write(b"This is not a PDF file")
+            tmp.flush()
+            tmp.seek(0)
+            files = {"file": (tmp.name, tmp.read())}
+            response = requests.post(
+                "http://doctor:5050/utils/document-number/pdf/",
+                files=files,
+            )
+        self.assertEqual(response.status_code, 400, msg="Wrong status code")
+
+
 class RedactionTest(unittest.TestCase):
     def test_xray_no_pdf(self):
         """Are we able to discover bad redacts?"""
diff --git a/doctor/views.py b/doctor/views.py
index 795248d..e9c685e 100644
--- a/doctor/views.py
+++ b/doctor/views.py
@@ -437,11 +437,20 @@ def get_document_number(request) -> HttpResponse:
     :return: PACER document number
     """
 
-    form = BaseFileForm(request.GET, request.FILES)
+    form = BaseFileForm(request.POST, request.FILES)
     if not form.is_valid():
-        validation_message = form.errors.get_json_data()["__all__"][0][
-            "message"
-        ]
+        error_data = form.errors.get_json_data()
+        if "__all__" in error_data:
+            validation_message = error_data["__all__"][0]["message"]
+        elif "file" in error_data:
+            validation_message = error_data["file"][0]["message"]
+        else:
+            for field, errors in error_data.items():
+                if errors and errors[0]:
+                    validation_message = errors[0]["message"]
+                    break
+            else:
+                validation_message = "Form validation failed."
         return HttpResponse(validation_message, status=BAD_REQUEST)
     fp = form.cleaned_data["fp"]
     document_number = get_document_number_from_pdf(fp)