= Solution
The PDF's apex angle is $30^\circ$, so each contacted face makes $\alpha=15^\circ$ with the vertical. Let N be the inward <normal force> per face. Its vertical component is downward, $-N\sin\alpha$; limiting upward <static friction> contributes $\mu N\cos\alpha$. Symmetric contacts cancel horizontal forces and torque. Incipient lift consequently requires
$$
\boxed{N_{\min}=\frac{mg}{2(\mu\cos\alpha-\sin\alpha)}\simeq3.08\,\mathrm N\quad\text{per face}.}
$$
This is the usual \b[normal gripping force] convention, using $g=9.81\,\mathrm{m\,s^{-2}}$. Friction can lift the prism only if $\mu>\tan\alpha$, which is satisfied here.
If “force applied” means the magnitude of the entire finger-contact resultant, including its tangential component, the <normal versus resultant force in a frictional pinch> gives
$$
\boxed{F_{\min}=N_{\min}\sqrt{1+\mu^2}=3.31\,\mathrm N\quad\text{per face}.}
$$
The optimal resultant lies at the limiting <friction angle> $\arctan\mu$ from the inward normal. Stating which force is being measured avoids confusing these two legitimate quantities.
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