fix: Reset PDF stream position to the beginning before reading to ensure correct processing.

models/sign_document.py

@@ -30,6 +30,7 @@ class SignDocument(models.Model):
             return base_output
 
         try:
+            base_output.seek(0)  # IMPORTANT: Reset stream position to start
             base_pdf = PdfFileReader(base_output, strict=False)
         except (ValueError, PdfReadError):
             return base_output