The PDF file may come in a variety of formats, such as single page PDF or a multi page PDF. How they are opened will not vary but the initial dialog will be slightly different with a multi-page document showing thumbnails for all the items included in the file and a single one, just a single image of the included vector.
Once you have opened the PDF, you can then copy the item to another open document or perhaps save the item to the CC libraries for use in other apps.
With PDF Photoshop open, you will also have to specify
as well as the thumbnail size
You can also use the place embedded or linked menu command to add the item to an existing document. There is no additional dialog if the item is a single page file but there is a dialog for a multiple page (you can set the thumbnail size) to allow for the selection of a particular vector (sadly it does not allow for multiple items)
Once opened, the item can be re-sized from the default size which may be the same size as the document or smaller - to bigger or smaller than the current document. You can re-size at any point. You can also then add effects (it is a smart object)
Loaded as a placed item