InDesign files are INDD, but can only be created in ID.
PDFs can be exported from or placed into an INDD.
I think you should start with some classes. InDesign is a very complex program which needs some intensive learning.
As mentioned, InDesign has a steep learning curve. You'll need some lessons, such as:
http://www.lynda.com/InDesign-tutorials/Getting-Started-InDesign/164745-2.html?srchtrk=ind ex:1%0Alinktypeid:2%0Aq:getting%2Bstarted%2Bwith%2Bindesign%0Apage:1%0As:relevance%0Asa:tr ue%0Aproducttypeid:2
It may be more cost-effective for your employer to pay for a professional designer to handle their projects, the artwork is only one part of the production process and if handled badly can cause expensive problems at the printing stage.
And PDFs are not for editing. You don't start with them for anything. You can place them as graphics in a page.