This method creates a PDF file and returns the binary PDF data as a byte array. This particular line of code supposes that the resulting file is small and fits into the available heap memory, but if this code can not make this 100% sure, then it is vulnerable to an out of memory condition.
byte pdf = toPdf(file);
Moreover if it run server-side, that means in general many parallel threads. Bulk data should never by handled by byte arrays.
Streams should be used and the data should be spooled to disk or database.