Typically the size of the PDF does not grow very much (remember that it is a repeating line thousands of times). The compresion in the PDF reduces the multiple lines to a single string so the size does not get impacted very much.
Sounds like you may have a different issue. Can you post one of those large PDFs and we can see what is it it. If you do not want to post it in this public forum send it to firstname.lastname@example.org.