To simplify the expression \( 7^{-3} \cdot 7^{-5} \) using the properties of exponents, we can apply the rule that states \( a^m \cdot a^n = a^{m+n} \).
In this case, we have:
\[ 7^{-3} \cdot 7^{-5} = 7^{(-3) + (-5)} = 7^{-8} \]
To express \( 7^{-8} \) with positive exponents, we use the property that \( a^{-n} = \frac{1}{a^n} \):
\[ 7^{-8} = \frac{1}{7^8} \]
Thus, the expression \( 7^{-3} \cdot 7^{-5} \) with positive exponents only is:
\[ \frac{1}{7^8} \]