I noticed that after compiling a document using TeXWorks and PDFLaTeX (I made a clean install less than a month ago) there seems to be a strange kerning issue whenever "f" and "i" appear next to each other in textmode and I have no idea what is causing it. If I compile the text and try to highlight it in a pdf reader, it seems to treat "fi" as its own character and I cannot highlight just the "f" or the "i". In all other cases the kerning seems fine.
\documentclass[11pt]{amsart}
\usepackage{graphicx}
\usepackage{epstopdf}
\usepackage{amsthm}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{amsxtra}
\usepackage{amscd}
\usepackage{verbatim}
\usepackage{rotating}
\usepackage{multirow}
\usepackage{multicol}
\usepackage{url}
\usepackage[all]{xy}
\begin{document}
identities for modified lattice paths by establishing a bijection
\end{document}