The default mechanism for creating search strings and for doing the actual search related to a file link may not work correctly in all cases. For example, BibTeX database files have many entries like ‘year="1993"’ which would not result in good search strings, because the only unique identification for a BibTeX entry is the citation key.
If you come across such a problem, you can write custom functions to set
the right search string for a particular file type, and to do the search
for the string in the file. Using
add-hook, these functions need
to be added to the hook variables
org-execute-file-search-functions. See the docstring for these
variables for more information. Org actually uses this mechanism
for BibTeX database files, and you can use the corresponding code as
an implementation example. See the file org-bibtex.el.