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 CS3 before you convert the document. (See Configure plug‑ins.)
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 CS3, 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 CS2 can’t open InDesign CS3 documents directly. You must update InDesign CS2 with special plug‑ins and choose File > Export in InDesign CS3 to save documents in INX format before opening them in previous versions. (See Save backwards to previous InDesign versions.)