When I set up an in-place ediscovery search, if I tell the search dialog that I only want to search "documents", does that restrict the search to only at

Good Afternoon,

Yes it restricts the search to 'attached documents'.

The article below should clarify the process for you.

In-Place eDiscovery and In-Place Hold in the New Exchange

http://blogs.technet.com/b/exchange/archive/2012/09/26/in-place-e-discovery-and-in-place-hold-in-the-new-exchange.aspx

Hi,

I recommend you look at the following article,there are detailed description

http://technet.microsoft.com/en-us/library/dd298021.aspx

Search query   You can either include all mailbox content from the specified mailboxes or use a search query to return items that are more relevant to the case or investigation. You can specify the following parameters in a search query:

• Keywords   You can specify keywords and phrases to search message content. You can also use the logical operators AND, OR, and NOT. Additionally, Exchange 2013 also supports the NEAR operator, allowing you to search for a word or phrase that's in proximity to another word or phrase.
  To search for an exact match of a multiple word phrase, you must enclose the phrase in quotation marks. For example, searching for the phrase plan and competition returns messages that contain an exact match of the phrase, whereas specifying plan AND competition returns messages that contain the words plan and competition anywhere in the message.
  Exchange 2013 also supports the Keyword Query Language (KQL) syntax for In-Place eDiscovery searches

Thanks.