Most of the search commands only read plain text files and not PDFs. To search PDF files from the terminal, you can use pdfgrep. Learn about pdfgrep here.
grep is a reliable tool for in-depth file searching. The following tools extend grep’s functionality and wrap it in a full-fledged graphical interface.
If you have used the Linux command line before, you’ve no doubt used “grep” to search for strings of text. There’s a better way to do so, and it’s called Ack.