Dragging file at the Dock creates a copy of a file?
Dragging a file/folder into the Dock just creates a reference there, it does not duplicate the file/folder. In your case you can omit the "create a link" step.

The reference to said object is stored in the $HOME/Library/Preferences/com.apple.dock.plist file under the persistent-others key as a Dictionary labeled Item N where N is the next available number starting from 0.  Among the information stored about the object is its pathname so the object can be opened when its Dock Tile is clicked.

    &lt;key&gt;persistent-others&lt;/key&gt;
    &lt;array&gt;
            &lt;dict&gt;
                    &lt;key&gt;GUID&lt;/key&gt;
                    &lt;integer&gt;86167247&lt;/integer&gt;
                    &lt;key&gt;tile-data&lt;/key&gt;
                    &lt;dict&gt;
                            &lt;key&gt;arrangement&lt;/key&gt;
                            &lt;integer&gt;2&lt;/integer&gt;
                            &lt;key&gt;displayas&lt;/key&gt;
                            &lt;integer&gt;1&lt;/integer&gt;
                            &lt;key&gt;file-data&lt;/key&gt;
                            &lt;dict&gt;
                                    &lt;key&gt;_CFURLAliasData&lt;/key&gt;
                                    &lt;data&gt;
                                    AAAAAACkAAMAAQAA0HpGVwAASCsAAAAAABuw
                                    VwAxxNoAANB6bMcAAAAACSD//gAAAAAAAAAA
                                    /////wABAAgAG7BXABsCdgAOABQACQBEAG8A
                                    dwBuAGwAbwBhAGQAcwAPABoADABNAGEAYwBp
                                    AG4AdABvAHMAaAAgAEgARAASABNVc2Vycy9w
                                    c2UvRG93bmxvYWRzAAATAAEvAAAVAAIACv//
                                    AAA=
                                    &lt;/data&gt;
                                    &lt;key&gt;_CFURLString&lt;/key&gt;
                                    &lt;string&gt;file:///Users/pse/Downloads/&lt;/string&gt;
                                    &lt;key&gt;_CFURLStringType&lt;/key&gt;
                                    &lt;integer&gt;15&lt;/integer&gt;
                            &lt;/dict&gt;
                            &lt;key&gt;file-label&lt;/key&gt;
                            &lt;string&gt;Downloads&lt;/string&gt;
                            &lt;key&gt;file-mod-date&lt;/key&gt;
                            &lt;integer&gt;3497684167&lt;/integer&gt;
                            &lt;key&gt;file-type&lt;/key&gt;
                            &lt;integer&gt;2&lt;/integer&gt;
                            &lt;key&gt;parent-mod-date&lt;/key&gt;
                            &lt;integer&gt;3497684167&lt;/integer&gt;
                            &lt;key&gt;preferreditemsize&lt;/key&gt;
                            &lt;integer&gt;-1&lt;/integer&gt;
                            &lt;key&gt;showas&lt;/key&gt;
                            &lt;integer&gt;1&lt;/integer&gt;
                    &lt;/dict&gt;
                    &lt;key&gt;tile-type&lt;/key&gt;
                    &lt;string&gt;directory-tile&lt;/string&gt;
            &lt;/dict&gt;
    &lt;/array&gt;