Setting "compatibility" parameter requires having a PDF structure that

has NOT had PDF_open_*() called on it, according to the documentation.

There is not currently any way to obtain such from user-land in PHP.
@ Catch users trying to set "compatibility" parameter, which is not
@ supported from user-land.
#
# Not sure this is the best way to do this...
# Uwe, could you please double check this?

ext/pdf/pdf.c

@@ -1844,6 +1844,11 @@ PHP_FUNCTION(pdf_set_parameter) {
 		RETURN_FALSE;
 	}
 
+    if (arg2->value.str.val == "compatibility") {
+		php_error(E_ERROR,"Compatibility modes not supported at this time");
+		RETURN_FALSE;
+	}
+	
 	PDF_set_parameter(pdf, arg2->value.str.val, arg3->value.str.val);
 
 	RETURN_TRUE;