diff --git a/changedetectionio/content_fetchers/base.py b/changedetectionio/content_fetchers/base.py
index 73b69a18a..942a372f9 100644
--- a/changedetectionio/content_fetchers/base.py
+++ b/changedetectionio/content_fetchers/base.py
@@ -87,6 +87,8 @@ class Fetcher():
     favicon_blob = None
     instock_data = None
     instock_data_js = ""
+    # Original response bytes (needed for PDF etc), fetchers that can't provide them leave this as None
+    raw_content = None
     screenshot_format = None
     status_code = None
     webdriver_js_execute_code = None
@@ -151,8 +153,7 @@ class Fetcher():
         Call this after content has been saved to disk.
         """
         self.content = None
-        if hasattr(self, 'raw_content'):
-            self.raw_content = None
+        self.raw_content = None
         self.screenshot = None
         self.xpath_data = None
         # Keep headers and status_code as they're small
diff --git a/changedetectionio/processors/text_json_diff/processor.py b/changedetectionio/processors/text_json_diff/processor.py
index 13de489e2..0b9efb9ad 100644
--- a/changedetectionio/processors/text_json_diff/processor.py
+++ b/changedetectionio/processors/text_json_diff/processor.py
@@ -43,6 +43,11 @@ class PDFToHTMLToolNotFound(ValueError):
         ValueError.__init__(self, msg)
 
 
+class PDFNotAvailableFromFetcher(ValueError):
+    def __init__(self, msg):
+        ValueError.__init__(self, msg)
+
+
 class FilterConfig:
     """Consolidates all filter and rule configurations from watch, tags, and global settings."""
 
@@ -481,6 +486,12 @@ class perform_site_check(difference_detection_processor):
 
         # PDF preprocessing
         if watch.is_pdf or stream_content_type.is_pdf:
+            # Browsers show PDFs in their built-in viewer, so a fetcher may only have the viewer's HTML
+            if not self.fetcher.raw_content or b'%PDF' not in self.fetcher.raw_content[:1024]:
+                raise PDFNotAvailableFromFetcher(
+                    "Content is a PDF but this fetcher could not provide the original PDF file, "
+                    "try the 'Basic fast Plaintext/HTTP Client' fetcher instead."
+                )
             content = content_processor.preprocess_pdf(raw_content=self.fetcher.raw_content)
             stream_content_type.is_html = True