If the document is not showing in the search results there are some things to be considered.
1) If the document is just uploaded. If the document is just uploaded it will not be available immediately in the search results. It will be available after the followed incremental crawl. By default the incremental crawl occurs once in 20 minutes.
2) Concerned person has permissions for the document: He/she searching for the doucment must have minimum read permissions for that document in order to see in the search results.
3) Draft Version of the document: If the document is checked out to a user or if the document is in "Draft version" (Waiting for an approval) the document won't be shown up in the search results.
4) Make sure the file type is indexed by the search server. For example if the file type is pdf by default this type is not indexed by the search server. For that the PDF component called IFileter needs to be installed in order to query and index the PDF content.