Gmail has constantly improved its search technology, but there’s something you couldn’t do until recently: search inside attachments. Sure, you could find an attachment if you knew the filename or some keywords from the message. If someone sent you a text file or an HTML file, Gmail indexed its content, but Gmail couldn’t index PDF files, Word documents, PowerPoint presentations and other popular attachment formats.
The good news is that Gmail has finally added support for searching inside attachments. I’ve just tested this feature for .pdf files, .doc documents, .ppt presentations and it works, even though some old attachments may not be indexed yet.
To find messages that have attachments, search for has:attachment and add some keywords to your query. To restrict your search to PDF files, search for has:attachment filename:pdf.
As you can see from the screenshot, Gmail found a message with no text in the body and no subject. Obviously, Gmail indexed the PowerPoint attachment.