Page limit sign failure on 3Mb text file (with 100+ pages)

Page limits make zero sense in a digital age. My computer does not get full of pages, it gets full of bytes. I just had Adobe self-sign refuse to accept and certify a 3 Mb (megabyte, not gigabyte) document signature and save as read-only. The document is a journal, comprised of short text pages and zero images. In what universe is a 3 Mb document too big to handle? This is a major Adobe fail. Any suggestions (I have Adobe cloud at $700/year as an individual creator, so "upgrade your account more" is not a reasonable answer.