6. As shown in Figure 2, the convex quadrilateral $A B C D$ is inscribed in a circle, $A B$ and $D C$ intersect at point $P$, $B C$ and $A D$ intersect at point $Q$, $P E$ and $Q F$ are tangent to the circle at points $E$ and $F$ respectively. Then, $P Q$, $P E$, and $Q F$ can form a ( ) triangle.
(A) Acute
(B) Right
(C) Obtuse
(D) None of the above
6. B.

Take a point $K$ on $P Q$ such that $P, B, C, K$ are concyclic. At this time,
$$
\begin{array}{l}
\angle C K P=\angle A B C=\angle C D Q \\
\Rightarrow Q, D, C, K \text{ are concyclic. }
\end{array}
$$
$$
\begin{array}{l}
\text{Then } P E^{2}+P F^{2}=P C \cdot P D+Q C \cdot Q B \\
=P K \cdot P Q+Q K \cdot Q P \\
=P Q(P K+Q K)=P Q^{2} .
\end{array}
$$