Convert earlier versions of InDesign documents
To
convert previous versions of InDesign documents to the current version, choose
File > Open and open the file. Keep in mind the following points:
If you used third-party plug-ins to create
an earlier version of a document, check with the manufacturer to
make sure that they are installed correctly for and are compatible
with InDesign CS4 before you convert the document.
When you convert a document, you may see an alert
message asking if you want to use the exception word list in the
user dictionary or the one in the document. For information about
this alert message, see Choosing word lists when opening documents.
Library files created in earlier versions of InDesign
will open and convert in InDesign CS4, even if the library
is locked. You have to specify a name and location for the converted
library files; the default naming convention is filename‑X.indl.
InDesign CS4 can’t open InDesign CS3
documents directly. You must update InDesign CS3 with special plug‑ins
and choose File > Export in InDesign CS4 to save documents
in INX format before opening them in previous versions. (See Save backwards to the previous InDesign version.)

If you’re experiencing problems with
the document created in a previous version of InDesign, use the
Export dialog box to save the document in InDesign Markup (IDML)
format. Then open the IDML file and save it as an InDesign document.