exec error: Error: spawn pdftk ENOENT [REOPEN] (WINDOWS)

[ThatBrianDude]

exec error: Error: spawn pdftk ENOENT
C:\Users\User\Documents\Instant-Tester\commands\testme.js:29
if (err) throw err
^

Error: spawn pdftk ENOENT
at Process.ChildProcess._handle.onexit (internal/child_process.js:240:19)
at onErrorNT (internal/child_process.js:415:16)
at process._tickCallback (internal/process/next_tick.js:63:19)

Getting this on windows.
I've installed the PDF Toolkit and the server from here:
https://www.pdflabs.com/tools/pdftk-the-pdf-toolkit/