Interesting and original proposal. The report starts with the theory (madlung fluid, ether, negative mass)
Since negative mass can’t be synthesized yet in lab conditions, the author of the report claims it can be found at the center of planets and other solid formations since the positive mass would crowd out the negative one and push it to the center. In the end the author proposes drilling a tunnel to the center of the moon where a negative mass glut is expected to be found. For practical reasons drilling one here on earth is technically not feasible. But with a drilling company and some nukes, calculations show it can be done.
The theory presented in the report seems to be old and suffers from early problems that have discredited negative energy. But with minor corrections everything stated in the report is very plausible.
https://www.dia.mil/FOIA/FOIA-Electronic-Reading-Room/FileId/170039/