The principle of how to convert BCD to Binary is illustrated in my post quoted above. But in that case, the enquirer only wanted to convert numbers between 00 and 31 (ie. day of the month digits)
Binary = U + 10 * T + 100 * H + 1000 * M where U = the units digit in BCD, T = the tens digit, H = the hundreds digit and M = the thousands.
So in the circuit quoted, I converted the Tens BCD digit to 00, 10, 20 or 30 depending on the BCD tens digit and then added it to the units digit.
So to cover the full range of tens digits, you will have to design logic to do this conversion (ie. if the tens BCD digit is 4, generate 40 in binary and input it to the adder, etc). Repeat the exercise for the Hundreds and Thousands digits. Then add them all together.
Another way to do it would be to use 4 presettable decade counters (configured to count down) and a binary counter (configured to count up). Preset the decade counters with the BCD digits and reset the Binary counter. Then apply clock pulses to both counters. When the Decade Counter = 0, stop the counting and the binary counter will indicate the binary value of the BCD digits.
Len