Many iOS users are heavy Gmail users. The latter’s iOS app was updated for the iPhone 5 recently and is still by far the best way to search for emails on the go. Now, it appears Google has added support to allow for searches of text within attachments, according to Google Operating System (via LifeHacker):
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:attachmentand add some keywords to your query. To restrict your search to PDF files, search for has:attachment filename:pdf.
I tested this on my Mac and also within the Gmail iOS app. It works exactly as described, and specific keyword search results turned up attachments containing my search query, even when emails had no text or named attachments. This is a particularly handy feature that expands search capability within Gmail, especially when attachments aren’t properly named but contain what you are looking for.
Let me know if it works for you!