These are the computer-fillable forms. If you want the forms to calculate for you, or if you want to save the form to your computer with your filled-in data, then you need use Adobe Acrobat Reader to fill it out. If you don't care about those features (calculate or save), you can use most any PDF-viewer to fill them out; if so, you won't need to use these instructions and can just click on the form's link as usual.
If you DO want to use Adobe Acrobat Reader to fill in the form, you should right-click the file in the browser and save it to your computer. Then start Adobe Acrobat Reader and go to File > Open an0d select the file you saved.
** Alternately, navigate to the folder where you saved the file. Right-click on the file and select Open with > Adobe Acrobat Reader
Most computers have Adobe Acrobat Reader installed. If yours doesn't, go here: Adobe Acrobat Reader. The CCA forms are compatible with Adobe Reader version 9 and up, so you don't need the most recent version (version "DC") to use them.