I'd like to share some information and tips for ebook reading that I've discovered so far.
1. File formats
Most widely supported ebook file formats are ePub and Mobi. (Check this wikipedia page.) Many apps are available to read ebooks on electronic devices such as iPad, tablets and cell phones based on Android platform, and needless to say, PC, and so on. For example, amazon.com provides Kindle-book (file extension .azw) apps for various environments (download).
2. Useful apps
calibre (free) is useful to manage ebook collections, to read, to change meta-data of ebook files, as well as to convert text files (doc, txt, rtf, html, etc) into ebook files. Mobipocket Creator (free) is also good.
3. Basic procedure to convert PDF files into ebook files
1) image PDFs : some scanned PDF files are actually composed of image files.
(Crop out the margin to remove headers and footers; this is to prevent things like page numbers appear in the converted files, as well as to remove the margin itself) → Convert the file into a text file via OCR programs → Edit the text file when necessary → Convert the edited text file into eBook files
2) text PDFs
(Crop out the margin) → Edit the text file when necessary→ Convert the edited text file into eBook files
3) text files (doc, rtf, html, txt, etc)
Convert the files into eBook file formats
4. Public domain anthropology ebooks on the internet
Project Gutenberg (here)
Digital Book Index (here)
Open Library (here) is also good though it doesn't provide the category "Anthropology"
Internet Archive (here) - the fun thing about this library's contents is that a few scanned books show the name of the original copy's owner. (You will find out when you see some of them.)