You should be able to use Filters right? 

var searchHits = client.Search<RemoteHostedContentItem>().Filter(x =>x.Field1.Match(value1) & x.Field2.Match(value2));

Hi. I would use _client.BuildFilter<RemoteHostedContentItem> to build out the filter based on the values that you know. An example of useage would be:

var query = _client.Search<RemoteHostedContentItem>().ExcludeDeleted().CurrentlyPublished();

// Check for values you know
// By wrapping in if statement
// filename is just an example add your fields here
if (!string.IsNullOrEmpty(filename)) 
{
	var NameFilter = _client.BuildFilter<RemoteHostedContentItem>().And(x => x.FileName.Match("filename"));
	query = query.Filter(NameFilter);
}

// Example to show adding another Filter to query
// Let's say your type implements this interface which allows you
// To hide a file from search
var SearchableFilter = _client.BuildFilter<IShouldSearch>().And(x => x.IsHiddenFromSearch.Match(false));

// Calling query.Filter multiple times on query adds the querys together, it does not replace the last one
query = query.Filter(SearchableFilter);

var results = query.Skip((page - 1) * pageSize).Take(pageSize).GetContentResult();

Hope this helps!

-John