pdfGetCapHeight

double __stdcall pdfGetAscent(PPDF IPDF);
double __stdcall pdfGetDescent(PPDF IPDF);
double __stdcall pdfGetCapHeight(PPDF IPDF);
int32_t __stdcall pdfGetIsFixedPitch(PPDF IPDF);

function pdfGetAscent(const IPDF: PPDF): Double; stdcall;
function pdfGetDescent(const IPDF: PPDF): Double; stdcall;
function pdfGetCapHeight(const IPDF: PPDF): Double; stdcall;
function pdfGetIsFixedPitch(const IPDF: PPDF): Integer; stdcall;

Purpose. Read the current font's ascent/descent/cap-height metrics and fixed-pitch (monospace) flag, all as fractions of the font's own em-square (typically scaled by the caller against the active font size).

Return value. The respective metric; 0.0/0 if IPDF is invalid or no font is currently selected.

C# (P/Invoke)

public static extern double pdfGetCapHeight(IntPtr IPDF);