If you cannot enter text or use the list fields on a form you have downloaded, the form is probably open in Preview and cannot be edited.  To edit your form you must open it in Adobe Reader. 

To open the form in Adobe Reader:

•      Move the cursor over the file you downloaded and press the CTRL button and the mouse:

•      A menu will be displayed.  Click on Open With:

•      Click on Adobe Reader.

The form will be opened with Adobe Reader and editable.  You can also change the default settings so that downloaded PDF forms always open in Adobe Reader.

To change the default settings:

•      Move the cursor over the file you downloaded and press the CTRL button and the mouse:

•      A menu is displayed.  Click on Get Info:

•      Select Adobe Reader from the Open With options and press the Change All button.

The default selection will be updated to always open PDF files with Adobe Reader.