PNG is 26 years old and basically unchanged since then. Same with 30 year old JPEG, or for those with more advanced needs the 36 year old TIFF (though there is a newer 21 year old revision). All three have stood the test of time against countless technologically superior formats by virtue of their ubiquity and the value of interoperability. The same could be said about 34 year old zip or 30 year old gzip. For executable code, the wine-supported subset of PE/WIN32 seems to be with us for the foreseeable future, even as Windows slowly drops comparability.
The latest Office365 Word version still supports opening Word97 files as well as the slightly older WordPerfect 5 files, not to mention 36 year old RTF files. HTML1.0 is 30 years old and is still supported by modern browsers. PDF has also got constant updates, but I suspect 29 year old PDF files would still display fine.
In 2005 you could look back 15 years and see a completely different computing landscape with different file formats. Look back 15 years today and not that much changed. Lots of exciting new competitors as always (webp, avif, zstd) but only time will tell whether they will earn a place among the others or go the way of JPEG2000 and RAR. But if you store something today in a format that's survived the last 25 years, you have good chances to still be able to open it in common software 50 years down the line.