sorting photos in a file

You haven't answered markwmsn's questions, so it's harder to help. Perhaps you are viewing pictures in the Photos app? And, by "file," did you mean Albums?

In Photos, the picture files are kept in the Library package in the Pictures folder on Finder. Images are kept in Albums for viewing. Some Albums, like Library and Recents, are provide by Apple with a pre-set structure and order that can't be changed. Albums that we users make, using the Photos menu File>New Album, can have whatever pictures we choose and can be sorted Oldest first or Newest first.

For an album of your own making, you can use the menu View>Sort to arrange your pictures for viewing.

If you want an album that has all your pictures in it that you can sort, then you can open Recents and do Select All, and then choose "File>New Album with with Selection."

I'm sorry if this doesn't address your problem. You may find this useful:

Photos User Guide for Mac - Apple Support

What sort of a "file" did you put them in? From where did you copy them? How? How were they sorted before you copied them, and how were they sorted afterwards?

If you're viewing the photos in the Library (Years/Months/Days) view you can only view them sorted by the Oldest Capture Date.

However, if you create a smart album like this:

which will automatically refresh upon any import into the library you can sort by any of these methods:

The following screenshot shows the different sort orders in the different views in a Photos library: