Declaration of the National Anti-Slavery Convention was written by William Lloyd Garrison for the formation of the American Anti-Slavery Society in December 1833. It was reprinted in The Liberator on December 14, 1833. It is now available in the Public Domain.
You can also use the Optimized PDF option to crank the size down in very targeted ways. Given the big before/after shift, the culprit is probably the image you're embedding. Try exporting that file in various formats (PDF, jpg, png) and then import it.
There are two main ways to effect the file size of a scanned PDF. The main way would be to lower the scan resolution. For most black and white documents you should not need more then 100dpi to get a good quality PDF. If the file size is still to large, next to the PDF file type option should be a Set button. When you click Set, there will be radio buttons for PDF Compression. The default is standard, and if you change it to high, it will reduce the file size.