If you use Google's webmail service, Gmail, you can now search attachments in your e-mail messages that are in formats from popular programs, such as Adobe Acrobat, Microsoft Office, and others.
To perform an attachment search, you need to type into the search bar the statement has:attachment and your search terms. For example, a search through all your attachments for the word Obama would look like this: has:attachment Obama. If you wanted to limit the search to just PDF files that contained the word Obama, the search would look like this: has:attachment filename:PDF Obama.
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Gmail adds support for search inside message attachments | PCWorld