"how do I attach 1099b pdf to my turbotax business return for corporation?"
The software is programmed to support uploading and attaching the transmittal file (Form 8453) after it has been signed, scanned, and saved as a file. It does not support attaching more than one file, however.
You can combine your 8453 and 1099-B pages, provided you have PDF editing software capable of doing so, and upload the resultant file in the 8453 upload section (see attachment for an example).
