How to Pin Most Used Files and Folders on Dock
In the Finder, you should be able to click and drag folders into the Dock. Another option is, within Finder, any folders in the sidebar under "Favorites" (where you usually see Documents, Pictures, etc.), you can right-click and select "Add to Dock." This will add it to your Dock in the lower right portion near Downloads and Applications.

Additionally, if you want to create a "general use" folder comprised of documents/files from several folders, you can do the following:


Create an empty folder.
In the Finder, locate the document you want access to.
Right click the document and select "Make Alias."
Drag and drop the Alias to the empty folder.
Add the folder to the dock.


The Alias should provide a dynamic link to the original file.