This is a kind of run-on sentence called a comma splice. So, it is not grammatically correct but people use comma splices all the time, and it is not a very bad grammar violation, usually.
The way attached is used here is also okay, because it is very common to use that word in this way when referring to an email attachment.
But let's make it a little clearer:
Attached (to this email) you'll find the continuation of the August 20th order invoices. Please print...--- I removed some capital letters because they were used unnecessarily, and I also added the word 'the'.