Hello LIL11, You are right. It is not possible to open a CC 2019 file in InDesign CC 2018. Today I have the same problem. Every time when adobe makes a new version it is not possible to oben a new file in an older software version. This is not very customer-oriented but this is adobe. And when you are working with CC 2019 it is not possible to put a CC 2018 file into a book. First you have to save the file in CC 2019. This is bullshit, ..... Every day i have to work with books in InDesign and now I have to save more than 20.000 files into the CC 2019 version. About your problem, if you want to open a CC 2019 file in CC 2018 you must save it as a IDML file. Then you can open the IDML file in CC 2018 and save it as a .indd file.
... View more