In case anyone gets confused, PDFTk Server is just the name for the CLI tool, which hasn't been updated in 10y+ (and annoying to compile due to newer GCC versions removing GCJ). The pdftk provided in various distros (incl. Debian, Fedora, Arch, NixOS) is pdftk-java, a 3rd-party pure Java port of the original tool.
In case anyone gets confused, PDFTk Server is just the name for the CLI tool, which hasn't been updated in 10y+ (and annoying to compile due to newer GCC versions removing GCJ). The pdftk provided in various distros (incl. Debian, Fedora, Arch, NixOS) is pdftk-java, a 3rd-party pure Java port of the original tool.