This extension convert HTML to NSAttributedString each other. It works on Swift4.

HTML_to_NSAttributedString.swift

extension String {
    func convertAttributedString() -> NSAttributedString?{
        let html = self._removePT()
        let encoded = html.data(using: String.Encoding.utf8)!
        let attributedOptions : [NSAttributedString.DocumentReadingOptionKey : Any] = [
            .documentType : NSAttributedString.DocumentType.html,
            .characterEncoding : String.Encoding.utf8.rawValue
        ]
        do {
            let attributedTxt = try NSAttributedString(data: encoded, options: attributedOptions, documentAttributes: nil)
            let lineHeightFixed = _fixLineHeight(attributedString: attributedTxt)
            return lineHeightFixed
        }catch let error as NSError {
            print(error)
            return nil
        }
    }
    
    fileprivate func _removePT() -> String{
        let pattern = "<style(.|\n)*style>"
        var ranges: [NSRange] = []
        _ = self.pregMatche(pattern: pattern, target: nil, ranges: &ranges)
        var targets: [NSRange] = []
        ranges.forEach{
            var ranges: [NSRange] = []
            _ = self.pregMatche(pattern: "font\\-size: \\d*.*pt", target: $0, ranges: &ranges)
            targets += ranges
        }
        
        let result = targets.reduce(self) { (result, range) -> String in
            result.pregReplace(pattern: "pt", with: "px", range: range)
        }
        return result
    }
    
    fileprivate func _fixLineHeight(attributedString: NSAttributedString) -> NSAttributedString{
        let mutable = NSMutableAttributedString(attributedString: attributedString)
        let range = NSRange(location: 0, length: mutable.string.count)
        mutable.enumerateAttribute(.paragraphStyle,
                                   in: range,
                                   options: [.longestEffectiveRangeNotRequired])
        { value, range, isStop in
            if let style = value as? NSMutableParagraphStyle {
                style.maximumLineHeight = 0
                style.minimumLineHeight = 0
                style.lineHeightMultiple = 0
                mutable.addAttributes([NSAttributedStringKey.paragraphStyle: style], range: range)
            }
        }
        return mutable
    }
    
    fileprivate func addCSSStyle(style: String) -> String?{
        let pattern = "<\\/style>"
        var range: [NSRange] = []
        _ = self.pregMatche(pattern: pattern, target: nil, ranges: &range)
        guard let styleRange = range.first else {return nil}
        let index = self.index(self.startIndex, offsetBy: styleRange.location)
        let collection = Array(style)
        var mutable = self
        mutable.insert(contentsOf: collection, at: index)
        
        return mutable
    }
}


extension NSAttributedString{
    func convertHTML() -> String?{
        let newStyle = "br {display: none;}"
        let documentAttributes: [NSAttributedString.DocumentAttributeKey : Any] =
            [.documentType: NSAttributedString.DocumentType.html]
        do {
            let htmlData = try self.data(from: NSRange(location: 0, length: self.length),
                                         documentAttributes: documentAttributes)
            guard let html = String(data: htmlData, encoding: .utf8) else {return nil}
            let removed = html._removePT()
            return removed.addCSSStyle(style: newStyle)
        }catch let error as NSError {
            print(error)
            return nil
        }
    }
}

// Supporting regular expression
extension String {
    func pregMatche(pattern: String, target: NSRange?, options: NSRegularExpression.Options = [], ranges: inout [NSRange]) -> Bool {
        guard let regex = try? NSRegularExpression(pattern: pattern, options: options) else {
            return false
        }
        let targetStringRange = target ?? NSRange(location: 0, length: self.count)
        let results = regex.matches(in: self, options: [], range: targetStringRange)
        for i in 0 ..< results.count {
            for j in 0 ..< results[i].numberOfRanges {
                let range = results[i].range(at: j)
                ranges.append(range)
            }
        }
        return results.count > 0
    }
    
    func pregReplace(pattern: String, with: String, range: NSRange, options: NSRegularExpression.Options = []) -> String{
        let regex = try! NSRegularExpression(pattern: pattern, options: options)
        return regex.stringByReplacingMatches(in: self, options: [], range: range, withTemplate: with)
    }
}

@Bigigrammer do you have any idea how to manage bullet points with sub-bullet points in them?
I have one case where in the text there are a few bullet points with sub-bullet points in it. After converting it from HTML string to NSAttributed sub-bullet point alignment gets changed.

Let me know if you have any solution for that