Move pictures from one catalogue to the other without loosing keywords/tags

. . .  and one other point.  Do you have a good reason to maintain separate catalogues?   It is not a recommended approach for most users.

Just to correct Michel's typo. error, saving the metadata to files with the Ctrl+W command does not transfer the album  and stack information imported to a different catalogue.  I would also add that face recognition information is not transferred via a file import.

However, when you import the files with saved metadata, you should be presented with a dialog that allows you to map the keywords to existing keyword tags in the target catalogue.  If you decline the option, the tags will be imported, as Michel says, to the Imported Keywords category.  You can then move the tag to your desired tag structure.

You can save metadata like tags, captions, notes or ratings into the files themselves (in the metadata header for jpegs, tiff, psd.. or in sidecar xmp files for raws).

Shortcut: Ctrl W on the selected files.

When you import those files in another catalog (or in a different managing software), those metadata will be imported.

In Elements they will appear in the category 'imported keywords'.

You can't recover other organization features like albums, stacks or version sets. Those are only kept in the catalogs;  and Elements can't export parts of catalogs like Lightroom can do.

Edit: You can't recover, sorry for the typo, thanks Greg for correcting.