100 Pa is a strange pressure to quote. Leakage at 50 Pa might be half or it might be a bit more: leakage is proportional to pⁿ where, for buildings, 0.5 < n < 1.0 depending on what sort of holes it has.

What does the 0.75 m³/(h·m) figure refer to? Is it the leakage for the length of window perimeter? E.g., a 1 m × 1 m window would be 4 m × 0.75 m³/(h.m) so 3 m³/h with an area of 1 m² so 3 m³/(h·m²)?

Can you put a link to the pdf, assuming you downloaded it.

The other pages are the same except for the last which details U values.

The industry standard for classification of window air permeability is EN 12207, as in the certificate
you’ve provided. It would typically be on a CE Declaration of Performance - (but not mandatory for the UK DoP) that every manufacturer should now be providing.

The testing is carried out as prescribed in EN 1026.
3m³/h m² overall window area & 0.75m³/h m opening joint length @100Pa is the maximum limit that has to be met to achieve Class 4. I would be sure that the tested window would have come in quiet a bit lower as it would be surprising not to get to Class 4 – particularly on a window that has been ‘prepared’ for such a test. On a good window the air leakage will be very close to the x-axis even at 600Pa -the actual testing involves pressure differentials of up to 600Pa. The reference air permeability for classification (comparative) purposes is 100Pa