The Bulgarian Противогаз ПДЕ-1 was one of the many copies of the U.S. ABC-M17 Field Protective Gas Mask.  Nearly identical to the Czech M-10, one notable difference (other than the color) was the use of a five point head harness instead of six.  This example was made in 1981.

Противогаз ПДЕ = "Gas Mask PDE"

Similar masks in my collection:  U.S. Army ABC-M17, U.S. Army M17A2, Czech M-10, Polish MP-4