C# - For loop becoming very slow after many loops

Question

I'm very very new to c#. I have currently written this piece of code that will essentially loop through paragraphs in a word document and search for any regex matches within a list of regexes. It starts off very fast but then becomes painfully slow after about 1000 paragraphs in. Does anyone know how I can optimise the below code to stop being so slow after looping many times?

Thanks in advance,

static List<MatchDetails> GetRegexMatchesContent(Word.Document document, List<string> regexes)
        {
            var matchDetails = new List<MatchDetails>(2000);
            // For each paragraph in word document, run regex searches.
            for (int i = 0; i < document.Paragraphs.Count; i++)
            {
                Console.WriteLine($"Processed Paragraph {i} of {document.Paragraphs.Count}");
                var rng = document.Paragraphs[i + 1].Range;
                // Loop through each regex input.
                foreach (string regex in regexes)
                {
                    // Match regexes on text.
                    MatchCollection matches = Regex.Matches(rng.Text, regex, RegexOptions.IgnoreCase);
                    foreach (Match match in matches)
                    {
                        foreach (Capture capture in match.Captures)
                        {
                            {
                                if (capture.Value != "")
                                {
                                    // Retrieve regex match information and save to MatchDetails List.
                                    string matchText = capture.Value;
                                    int matchPageNo = rng.Information[Word.WdInformation.wdActiveEndPageNumber];
                                    int matchLineNo = rng.Information[Word.WdInformation.wdFirstCharacterLineNumber];
                                    int matchCharNo = capture.Index;

                                    MatchDetails matchRow = new MatchDetails { matchText = matchText, documentSection = "Body Text", pageNo = matchPageNo, lineNo = matchLineNo, charNo = matchCharNo };
                                    matchDetails.Add(matchRow);
                                }
                            }
                        }
                    }
                }
            }

            return matchDetails;
        }