Is it possible to somehow optimize pdfreader itextsharp?

Question

C++ / C#

There is a method that many times, using rectangle, reads text from different pages of a pdf document. Accordingly, the larger the file, the slower everything is processed, I tried to use parallel.foreach, but it didn’t work out much, everything seems to rest on pdfreader.
The method is something like this:

var lst = new ConcurrentBag<Test3>();
using(var reader = new PdfReader(byteArr))
{
    Parallel.Foreach(areas, t => 
    {
        var pageSize = reader.GetPageSize(t.PageNumber);
        var rectangle = GetRectagle(t.AreaData, pageSize);
        var text = GetTextFromRectangle(reader, rectagle, t.PageNumber);
        lst.Add(text);
    }
}