I have posted before about the good work of Rob Bradshaw and Biblicalstudies.org.uk whose mission is to "to make high quality theological material freely available throughout the world, thus providing Bible teachers and pastors with the resources they need to spread the Gospel in their countries." To this end they make PDF copies of older, but still helpful, books available for free. Today, they posted a notice here of R. H. Charles' commentary on Daniel here. While this work represents an older generation of scholarship. it is still a thorough treatment of Daniel.