add openai pdf upload support

lib/custom_exceptions/pdf_processing_error.rb

@@ -0,0 +1,23 @@
+class PdfProcessingError < CustomExceptions::Base
+  def initialize(message = 'PDF processing failed')
+    super(message)
+  end
+end
+
+class PdfUploadError < PdfProcessingError
+  def initialize(message = 'PDF upload failed')
+    super(message)
+  end
+end
+
+class PdfValidationError < PdfProcessingError
+  def initialize(message = 'PDF validation failed')
+    super(message)
+  end
+end
+
+class PdfFaqGenerationError < PdfProcessingError
+  def initialize(message = 'PDF FAQ generation failed')
+    super(message)
+  end
+end