You cannot use 35mm film in a Diana without modification. The original Chinese-made 1960's Diana camera was chambered only for 120 roll film and probably will not accept the accessory 35mm film back that is currently manufactured for the newer Diana clones called Diana+ and Diana F+.
There is a competing Chinese plastic camera called the Holga 135BC which is chambered for 35mm film. Holga also made a 120 roll film model about the same time that the original Dianas were made.