To convert layer(s) to an editable smart object:
- In the Layers palette, hide unnecessary layers.
To convert just one layer, [Alt]-click its "eye" pictogram.
(On this screenshot, the layers "Background" and "Smart" are prepared for conversion.)
When converting a single-layered image, skip this step.
- In the Effects palette, double-click the "Editable Object" pictogram.
- As result, you have a layered smart object and backup copies of the source layers. Hide or delete those if needed.
NB This action saves the edited document as "Autosave.psd". Please do not forget to resave its under original name to proper directory.
NB2 On Macs, this function works in a different way.