How Can I Search A Specific Type of File in Mac? Is there any way to search a specific type of file using Spotlight? I remember there was a special command or something that I had to put in front of the search phrase but I cannot remember it now. 

For example, if I want to search only PDFs for a particular phrase in Spotlight, what would I do?
Search by Kind One of the most useful ways to narrow down a search is by using the kind: keyword. This allows you to restrict your list of results to a certain file format. For instance, if you type time machine kind:pdf, Spotlight will pull up only PDF files containing the words "time" and "machine". You can also limit your search to e-mail messages, music files, System Preferences, applications, and more.

While the original Spotlight recognized only a limited number of file types, the Leopard version can look for files created by specific applications, as well as certain file formats. Searching for kind:mp3 or kind:tiff will find files in one of those formats, and searching for kind:pages or kind:powerpoint will show only documents created in one of those programs. For a list of useful keywords, see “My Kind of Keyword.” But remember, for the keywords to work, you must have the appropriate categories enabled in Spotlight’s preferences.

you can get more info here or here.