Here's a frustrating problem: You have InDesign CS4, and your buddy needs your file, but has InDesign CS2. "Easy!" you think, "just save an InDesign Interchange (INX) file and send it to him."
Lo, wonder of wonders: InDesign saves an INX file that's compatible only with the immediately preceding version of InDesign. (As I found out the hard way today.) CS4 saves a file for CS3; CS3 saves a file for CS2. If you don't have both versions on your computer, you're out of luck. Way to Quark it up, Adobe.
An INX file is just a glorified XML file. And Adobe, clever lads and lasses they are, inserted a version number in the file. Adobe CS2 looks at the version number, sees that the INX file is targeted for CS3, and pops up an error message without even trying to open the file. Curses.
But Mike Rankin figured it out last November: Open the INX file with your favorite text editor (like TextMate or BBEdit) and change the version number. Replace line number 2 (which looks like this):
<?aid style="33" type="document" DOMVersion="6.0" readerVersion="5.0" featureSet="257" product="6.0(352)" ?>
<?aid style="33" type="document" DOMVersion="5.0" readerVersion="4.0" featureSet="257" product="5.0(662)" ?>
Easy peasy. Open the INX file in InDesign CS2, and you're good to go. Use caution, though: This works best for simple layouts. The more complex your layout, the more likely it will unexpectedly change when re-imported into a lesser version of InDesign.