I am not sure if this question qualifies here, but it seems odd to me letter 'f' often get messed up when copied from pdf text.
I do research as a student, and I read a lot of papers. This happens a lot when I want to copy the name of a paper to rename the pdf file.
For example, I opened the link a paper from built-in pdf display plug-in of Chrome on a Macbook Pro with OSX 10.9. Try copy the title of the paper and paste it. The 'f' in 'fluids' will be missing.