PowerGREP is primarily designed to work with plain text files, and it can process most of file formats. However, ppt happens to be one of the unsupported formats of PowerGrep. But PowerGrep can still search any unsupported formats as binary files. Here is how you can do so to search ppt files:
"You can search through the raw, non-decoded contents of files that PowerGREP cannot decode by turning on the option "search through binary files". The search match will be listed in the results in both textual and hexadecimal representation. If you double-click on the search match, the file editor will open the file in hexadecimal mode. The view is very similar to that of a hex editor. Depending on the kind of file you are dealing with, you can still get meaningful search results."