Abstract: The present invention can provide an extensible file format compatible with previous, current, and future versions of an application program. The present invention can comprise including file version watermarks in an original data file of an application program. The file version watermarks can indicate various properties of the original data file. The file version watermarks can include a high version watermark, a last version watermark, a low version watermark, a creation version watermark, and an object version watermark. Each file version watermark can indicate changes, additions, or deletions made to the file. The present invention can use the file version watermarks to determine whether the file, or particular information in the file, corresponds to the previous, active, or future versions of an application program. Accordingly, the present invention can then load or save the original data file based on a result of the determination.