Compare two drawings, free
Pick a page in each PDF: what changed shows in colour, red only in A, green only in B. No sign-in, and your PDFs never leave this computer.
Choose both drawings, or drop both PDFs at once: the earlier one becomes A.
Pick a page in each PDF: what changed shows in colour, red only in A, green only in B. No sign-in, and your PDFs never leave this computer.