PDFs

As well as being available on Kindle/Paperback, Google Play, iBooks and various other platforms, the following books and other tutorials are available in PDF format:

Altered Tuning References

Fourths Tuning (EADGCF)
New Standard Tuning
DADGAD
Open E Tuning
Open G Tuning
Open C Tuning
Alternate Tunings for the Creative Guitarist (contains all of the above tunings)

The Guitar Hacks Series

The Pentatonics Handbook
3NPS Scales
The Horizontal Soloing System
Simple Chord Tone Soloing System

Books

Hacking the CAGED System – Book 1
Hacking the CAGED System – Book 2
No Theory Guitar Soloing
Melodic Soloing in 10 Days
Escalas en Horas (2 Position Guitar Scale System en español)