How can I add text in the top right corner of a page _without_ using fancyhdr

Using atbegshi guarantees that the text block will not be modified in any way, as it acts by "overlaying", so to speak.

\documentclass[a4paper]{article}
\usepackage{atbegshi,picture}
\usepackage{lipsum}


\AtBeginShipout{\AtBeginShipoutUpperLeft{%
  \put(\dimexpr\paperwidth-1cm\relax,-1.5cm){\makebox[0pt][r]{\framebox{Copyright DTV}}}%
}}

\begin{document}

\lipsum

\end{document}

Every page of the document will bear the copyright notice.

Here's a simple example using the background package:

\documentclass{article}  
\usepackage{background}
\usepackage{lipsum}% just to generate filler text

\SetBgContents{some additional text}
\SetBgScale{1}
\SetBgAngle{0}
\SetBgPosition{current page.north east}
\SetBgHshift{-2cm}
\SetBgVshift{-1cm}

\begin{document}

\lipsum[1-3]

\end{document}

Here is a minimal example using the eso-pic package.

\documentclass{article}  
\usepackage{eso-pic}% http://ctan.org/pkg/eso-pic
\usepackage{lipsum}% http://ctan.org/pkg/lipsum

\begin{document}

\AddToShipoutPictureBG*{%
  \AtPageUpperLeft{%
    \hspace{\paperwidth}%
    \raisebox{-\baselineskip}{%
      \makebox[0pt][r]{Here is some interesting text}
}}}%

\lipsum[1-3]

\end{document}

\AddToShipoutPictureBG will print something on every page, while the starred version \AddToShipoutPictureBG* prints it on the current page only. Placement is possible with spacing commands, with the help of predefined locations (like \AtPageUpperLeft and the like). See the package documentation for more on this.

eso-pic also provides placement of contents in the foreground to overlay with the existing page layout (in contrast to placing something in the background layer as suggested above) using \AddToShipoutPictureFG or \AddToShipoutPictureFG* with similar connotations as above.