Springer has free PDF books for machine learning available.

Here is the complete list, enjoy.

Statistics and Analysis of Scientific Data
http://link.springer.com/openurl?genre=book&isbn=978-1-4939-6572-4

Modelling Computing Systems
http://link.springer.com/openurl?genre=book&isbn=978-1-84800-322-4

Search Methodologies
http://link.springer.com/openurl?genre=book&isbn=978-1-4614-6940-7

Linear Algebra Done Right
http://link.springer.com/openurl?genre=book&isbn=978-3-319-11080-6

Linear Algebra
http://link.springer.com/openurl?genre=book&isbn=978-3-319-24346-7

Algebra
http://link.springer.com/openurl?genre=book&isbn=978-1-4613-0041-0

Understanding Analysis
http://link.springer.com/openurl?genre=book&isbn=978-1-4939-2712-8

Linear Programming
http://link.springer.com/openurl?genre=book&isbn=978-1-4614-7630-6

Understanding Statistics Using R
http://link.springer.com/openurl?genre=book&isbn=978-1-4614-6227-9

An Introduction to Statistical Learning
http://link.springer.com/openurl?genre=book&isbn=978-1-4614-7138-7

Statistical Learning from a Regression Perspective
http://link.springer.com/openurl?genre=book&isbn=978-3-319-44048-4

Applied Partial Differential Equations
http://link.springer.com/openurl?genre=book&isbn=978-3-319-12493-3

Robotics
http://link.springer.com/openurl?genre=book&isbn=978-1-84628-642-1

Regression Modeling Strategies
http://link.springer.com/openurl?genre=book&isbn=978-3-319-19425-7

A Modern Introduction to Probability and Statistics
http://link.springer.com/openurl?genre=book&isbn=978-1-84628-168-6

The Python Workbook
http://link.springer.com/openurl?genre=book&isbn=978-3-319-14240-1

Machine Learning in Medicine — a Complete Overview
http://link.springer.com/openurl?genre=book&isbn=978-3-319-15195-3

Object-Oriented Analysis, Design and Implementation
http://link.springer.com/openurl?genre=book&isbn=978-3-319-24280-4

Introduction to Data Science
http://link.springer.com/openurl?genre=book&isbn=978-3-319-50017-1

Applied Predictive Modeling
http://link.springer.com/openurl?genre=book&isbn=978-1-4614-6849-3

Python For ArcGIS
http://link.springer.com/openurl?genre=book&isbn=978-3-319-18398-5

Concise Guide to Databases
http://link.springer.com/openurl?genre=book&isbn=978-1-4471-5601-7

Digital Image Processing
http://link.springer.com/openurl?genre=book&isbn=978-1-4471-6684-9

Bayesian Essentials with R
http://link.springer.com/openurl?genre=book&isbn=978-1-4614-8687-9

Foundations of Programming Languages
http://link.springer.com/openurl?genre=book&isbn=978-3-319-70790-7

Introduction to Artificial Intelligence
http://link.springer.com/openurl?genre=book&isbn=978-3-319-58487-4

Introduction to Deep Learning
http://link.springer.com/openurl?genre=book&isbn=978-3-319-73004-2

Linear Algebra and Analytic Geometry for Physical Sciences
http://link.springer.com/openurl?genre=book&isbn=978-3-319-78361-1

Applied Linear Algebra
http://link.springer.com/openurl?genre=book&isbn=978-3-319-91041-3

Neural Networks and Deep Learning
http://link.springer.com/openurl?genre=book&isbn=978-3-319-94463-0

Data Science and Predictive Analytics (sorry, only paid version now)
http://link.springer.com/openurl?genre=book&isbn=978-3-319-72347-1

Analysis for Computer Scientists
http://link.springer.com/openurl?genre=book&isbn=978-3-319-91155-7

Excel Data Analysis
http://link.springer.com/openurl?genre=book&isbn=978-3-030-01279-3

The Elements of Statistical Learning
http://link.springer.com/openurl?genre=book&isbn=978-0-387-84858-7

Introductory Time Series with R
http://link.springer.com/openurl?genre=book&isbn=978-0-387-88698-5

A Beginner’s Guide to R
http://link.springer.com/openurl?genre=book&isbn=978-0-387-93837-0

Introduction to Evolutionary Computing
http://link.springer.com/openurl?genre=book&isbn=978-3-662-44874-8

Data Analysis
http://link.springer.com/openurl?genre=book&isbn=978-3-319-03762-2

Linear and Nonlinear Programming
http://link.springer.com/openurl?genre=book&isbn=978-3-319-18842-3

Fundamentals of Robotic Mechanical Systems
http://link.springer.com/openurl?genre=book&isbn=978-3-319-01851-5

Data Structures and Algorithms with Python
http://link.springer.com/openurl?genre=book&isbn=978-3-319-13072-9

Introduction to Partial Differential Equations
http://link.springer.com/openurl?genre=book&isbn=978-3-319-02099-0

Methods of Mathematical Modelling
http://link.springer.com/openurl?genre=book&isbn=978-3-319-23042-9

LaTeX in 24 Hours
http://link.springer.com/openurl?genre=book&isbn=978-3-319-47831-9

Introduction to Statistics and Data Analysis
http://link.springer.com/openurl?genre=book&isbn=978-3-319-46162-5

Principles of Data Mining
http://link.springer.com/openurl?genre=book&isbn=978-1-4471-7307-6

Computer Vision
http://link.springer.com/openurl?genre=book&isbn=978-1-84882-935-0

Data Mining
http://link.springer.com/openurl?genre=book&isbn=978-3-319-14142-8

Computational Geometry
http://link.springer.com/openurl?genre=book&isbn=978-3-540-77974-2

Statistical Analysis and Data Display
http://link.springer.com/openurl?genre=book&isbn=978-1-4939-2122-5

Statistics and Data Analysis for Financial Engineering
http://link.springer.com/openurl?genre=book&isbn=978-1-4939-2614-5

Stochastic Processes and Calculus
http://link.springer.com/openurl?genre=book&isbn=978-3-319-23428-1

Statistical Analysis of Clinical Data on a Pocket Calculator
http://link.springer.com/openurl?genre=book&isbn=978-94-007-1211-9

Clinical Data Analysis on a Pocket Calculator
http://link.springer.com/openurl?genre=book&isbn=978-3-319-27104-0

The Data Science Design Manual
http://link.springer.com/openurl?genre=book&isbn=978-3-319-55444-0

An Introduction to Machine Learning
http://link.springer.com/openurl?genre=book&isbn=978-3-319-63913-0

Guide to Discrete Mathematics
http://link.springer.com/openurl?genre=book&isbn=978-3-319-44561-8

Introduction to Time Series and Forecasting
http://link.springer.com/openurl?genre=book&isbn=978-3-319-29854-2

Multivariate Calculus and Geometry
http://link.springer.com/openurl?genre=book&isbn=978-1-4471-6419-7