How do I find and select Text in a RichTextBox with C# when Index is larger than an Int

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C#2.0

C#

WinForms

RichTextBox

I would like to find and select the first occurrence of a Text in a RichTextBox with C# and then select all the other finds of the same portion of Text. I know that's simple to do as long the index doesn't outrun the Integer Range. But what to do if it does? The functions RichTextBox.Find() and RichTextBox.Select() support only Integers. Now my Text Files are quite a bit larger between 41 KB and 150 KB. The Integer is definitely to small for finding and selecting with the inbuilt functions.
What would I do instead? Does someone have a ready function call for this?
Found nothing else than the inbuilt RichTextBox functions on my search which are only valid for files smaller and equal 32 KB. I am a novice in coding and I have no idea how I could build my own functions for finding and searching a RTB without using an Integer but a long. There seem to be no overloads for these functions :(

I currently use an int16 otherwise I get an exception of type mismatch.
I'm on Net 2 with VS 2008. At me the Integer carries only 32768 characters. I want to save the whole search string in the int16 but can store only one char so far.
What am I doing wrong? Now I changed to int32 and it seems to compile.