Yes, Confluence can index attachments and will find their content in searches. The following file types are supported:
* Microsoft Word (.doc, .docx, ...)
* Text (incl. XML)
* Powerpoint (.ppt, .pptx, ...)
* Excel (.xls, .xslx, ...)
The topic is also dealt with in Atlassian Answers and in a Confluence documentation already.
This section of the official Confluence search documentation may be helpful as well:
To search the content of other attachment types, you will need to use an attachment content extractor plugin. For more information, take a look at the following:
1. Existing extractor plugins which you can install on your Confluence site. See this search on Atlassian Marketplace.
2. Guidelines on developing your own attachment content extractor plugin. See our developer documentation on extractor plugins.