how to edit a PDF file copied from a Dell laptop to my Macbook Air

What are your goals for the PDF when you use the term “edit?”

If you are talking about changing the actual PDF content, then that capability is not inherent to OS X, and will require an expenditure for a third party PDF Editor, which you can find in the OS X App Store by searching for PDF editor. Or purchase Adobe Acrobat Pro for OS X.

If instead, you simply want to layer some annotation, or comments onto the PDF, then Apple's Preview, Skim, or Adobe Acrobat Reader are capable.