The question isn't completely clear (particularly regarding what you want to display the form as a drop-down?), however to add to RedRaccoon _'s answer you may want to look at importing the the library file provided for building Document Library content. This import file is discussed and demonstrated in the following blog posts:
As a general rule I wouldn't recommend using the CrudService for all lists as it shouldn't be used when there is a more specific service that can handle data retrieval - which in this case would be the DocumentService.
There are some Document Library specific views available to use (such as AlfSimpleView, AlfDetailedView, AlfTableView, AlfFilmStripView and AlfGalleryView) or you can build your own view by configuring the AlfListView - examples are shown in the Aikau tutorial on GitHub as recommended by .
If you can describe your use case in more detail (for example step through the user interaction) then I will be able to provide more support with regards to the forms and drop-downs that you've referred to in your question.
