UIFont+PSPDF.m

@implementation UIFont (PSPDFAdditions)

// https://gist.github.com/nuthatch/7594460
static CGFloat PSPDFMultiplicatorForPreferredContentSize(void) {
    CGFloat multiplicator = 1.f;
    NSString *preferredTextStyle = UIApplication.sharedApplication.preferredContentSizeCategory;
    if ([preferredTextStyle isEqualToString:UIContentSizeCategoryExtraSmall]) {
        multiplicator = 0.9f;
    }else if ([preferredTextStyle isEqualToString:UIContentSizeCategorySmall]) {
        multiplicator = 0.95f;
    }else if ([preferredTextStyle isEqualToString:UIContentSizeCategoryMedium]) {
        multiplicator = 1.f;
    }else if ([preferredTextStyle isEqualToString:UIContentSizeCategoryLarge]) {
        multiplicator = 1.1f;
    }else if ([preferredTextStyle isEqualToString:UIContentSizeCategoryExtraLarge]) {
        multiplicator = 1.2f;
    }else if ([preferredTextStyle isEqualToString:UIContentSizeCategoryExtraExtraLarge]) {
        multiplicator = 1.25f;
    }else if ([preferredTextStyle isEqualToString:UIContentSizeCategoryExtraExtraExtraLarge]) {
        multiplicator = 1.3f;
    }
    return multiplicator;
}

static CGFloat PSPDFFontSizeForTextStyle(NSString *textStyle, BOOL *isBold) {
    PSPDFAssert(textStyle);
    CGFloat fontSize = 12.f;
    if ([textStyle isEqualToString:UIFontTextStyleHeadline]) {
        fontSize = 17.f;
        if (isBold) *isBold = YES;
    }else if ([textStyle isEqualToString:UIFontTextStyleBody]) {
        fontSize = 17.f;
    }else if ([textStyle isEqualToString:UIFontTextStyleSubheadline]) {
        fontSize = 15.f;
    }else if ([textStyle isEqualToString:UIFontTextStyleFootnote]) {
        fontSize = 13.f;
    }else if ([textStyle isEqualToString:UIFontTextStyleCaption1]) {
        fontSize = 12.f;
    }else if ([textStyle isEqualToString:UIFontTextStyleCaption2]) {
        fontSize = 11.f;
    }

    // Return sharp sizes.
    return floor(fontSize * PSPDFMultiplicatorForPreferredContentSize());
}

+ (UIFont *)pspdf_preferredFontWithName:(NSString *)name textStyle:(NSString *)textStyle {
    PSPDFAssert(name);
    PSPDFAssert(textStyle);
    BOOL isBold = NO;
    CGFloat fontSize = PSPDFFontSizeForTextStyle(textStyle, &isBold);
    UIFont *font = [UIFont fontWithName:name size:fontSize];
    if (isBold) font = font.pspdf_boldFont;
    return font;
}

+ (UIFont *)pspdf_systemFontOfDynamicSize:(CGFloat)fontSize {
    return [UIFont systemFontOfSize:fontSize * PSPDFMultiplicatorForPreferredContentSize()];
}

+ (UIFont *)pspdf_boldSystemFontOfDynamicSize:(CGFloat)fontSize {
    return [UIFont boldSystemFontOfSize:fontSize * PSPDFMultiplicatorForPreferredContentSize()];
}

- (UIFont *)pspdf_boldFont {
    UIFontDescriptor *descriptor = [self fontDescriptor];
    descriptor = [descriptor fontDescriptorWithSymbolicTraits:descriptor.symbolicTraits|UIFontDescriptorTraitBold];
    return [UIFont fontWithDescriptor:descriptor size:0]; // Pass 0 to keep the same font size
}

@end