I attached a PDF of my brokerage summary 1099-B to my return but I am still being asked to send in Form 8453. Do I still need to send this in??

According to the first page of Form 8453:

 

FILE THIS FORM ONLY IF YOU ARE ATTACHING ONE OR MORE OF THE FOLLOWING FORMS OR SUPPORTING DOCUMENTS:

 

Form 8949, Sales and Other Dispositions of Capital Assets (or a statement with the same information), if you elect not to report your transactions electronically on Form 8949. 

 

Based on the information you have provided, it sounds like you should file this form.