Thank you, @Handoko and @jwdietrich.
"A reporting engine [with PDF support] that does not have GUI dependencies" is something I was looking for.
Though, I just need to convert plain text file into PDF file. In the mean time, I think I will just stick to my own txt2pdf by looking up PDF File Format 1.7 Specification.
However, it is good to know that professional PDF libraries for Free Pascal are available or going to be officially made available.