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.
You need a virtual PDF printer or PDF authoring tool to change the page size of a PDF file. Some applications like Adobe Acrobat and goPDF install a virtual printer that you can use to convert a document or image into a PDF file using any application with a Print function.