.NET - a good solution for finding specific keywords in long text input

I'm looking for a good way to implement specific keywords search in given text input, that would work with .net core web solution. Input text is going to be pretty long (like a html file or a long article), and I want to look for predifined keywords (around 1k keywords) in it, so I'd like to avoid working on raw strings. I tried to use elasticsearch for it, but in my case I want to find exact matches for specific keywords, which I'm not sure elasticsearch is good for.

Example: keywords data set: C#, C++, python, javascript, ios, java, objective-c

Example text input: (...) Our company specializes in writing solid C# and C++ solutions, anyone who is interested can apply for job today. We're also looking for java programmers.

Desired output for this example: C#, C++, java

Elasticsearch solution would also return 'ios', 'objective-c' and 'javascript' keywords, as parts of this keywords are present in input text (i tested multiple analyzers with both analyzed and text indexes with similar results). Currently my tags are stored in elasticsearch index, but I'm open to move them somewhere else.