Since RTF is a mostly textual file format, noticing plaintext strings in it is not unheard of, and shouldn't be treated as cause for suspicion.
otkloadr.dll is a library used for Visual Studio / office integration, as part of a package called "Microsoft Visual Studio Tools for the Microsoft Office System".
That package is used to incorporate Visual Studio components inside Office documents (such as rtf files), and to generate/manipulate Office files programmatically from within Microsoft development environments.
It might be used in an rtf document generated automatically directly by Microsoft-provided development tools or by a third party tool using Microsoft's office integration library (most third party office related manipulation tools are using this internally, and usually simply provide a different interface, probably in a different programming language).
It might also be used in an rtf using one of the advanced features "Microsoft Visual Studio Tools for the Microsoft Office System" brought into Office, or was converted from a newer format that did.
Inspecting the file format is needed to reach these conclusions with a higher degree of certainty. Since RTF is as mentioned a textual format this shouldn't be too complicated. Additionally, googling for RTF file parser yields multiple promising results.