I do not know about the mark in particular, but the late 1970s through the late 1980s were an especially difficult and sometimes violent chapter in Bolivia's histor with control of the government going back and forth between socialists and military coups combined with cocaine cartels and Bolivia being the poorest country in South America facing petroleum import shocks. The result was unstable currency and at times hyperinflation. A new government was put into power in October of 1982 and my guess is that the markings on your cover refer to steps they were taking to try to bring rapid inflation under control.
Many thanks for the reply. It definitely looks like its connected to the Hyperinflation period of Bolivia. Just trying to figure out if they were checking for stamps or currency or other specific artifacts. I have seen similar covers all bearing La Paz frankings. Hardly any information on the internet though as to the background of this exercise.
Means that the letter was open to control the contain,knowing that in the late 60's 70's and early 80's south america was under military governments almost all over,and they had taken all administrations,in order to fallow dissidents they open all suspected letters