Only the Form 1040 and any other forms or schedules which have an Attachment Sequence Number located in the upper right corner of the form or schedule. All other pages are worksheets and information only pages which are not needed to be sent.
Most likely, you downloaded the final PDF. That will include all calculation forms and worksheets. Depending on the types and sources of income you had in 2020, I would expect no more than the first 15 pages should be needed.
Basically, you need the base 1040 form (2 pages) and any of the schedules printed. For example, SCH C if you had self-employment income, SCH E if you had rental income, SCH F if you had farming income, etc. There's also the numbered schedules 1 thru 6. Any of those that you have should be included also.
the 1040 and any form or schedule that has an attachment sequence number is part of the filed return (upper right)