Installed using instructions from several posts by Thaddy as follows:
1. Add stretch-backports to sources.list
Create: sudo nano /etc/apt/sources.list.d/backports.list
Add: deb http://ftp.debian.org/debian stretch-backports main
Update: sudo apt-get update
Ignore complaints about not signed
2. FPC 3.0.4 and Lazarus 1.8.4 are both in stretch-backports
Use apt or apt-get, need to install with the -t option.
Answer Y to install without verification.
sudo apt-get -t stretch-backports install fpc
sudo apt-get -t stretch-backports install lazarus
Ignore complaints about not verified