6. The Tools in the Toolbox / 6.2 Tools for All Kind of Layers
The Placeholder Layer tool is used to create placeholder layers (see chapter 2.3.7). In the Tool Settings the option Show File Panel allows you to choose whether a file is inserted directly after creation.
If you create an empty placeholder layer, you can fill it later by dragging a file to it. Alternatively, you can double-click the File entry in the Layer Attributes (see chapter 4.11).