Can I print a custom paper on standsard size in word?
Solution 1:
If you do not want Word to scale (shrink) the document when you print it you should disable zoom or scaling in the print options.
For Microsoft Word 2003, go to Office Icon -> Print. In the dialog that appears, select "No Scaling" for the "Scale to paper size option". Note that depending on what your printer limits and your document margins are, this could leave parts of your document cropped off.
If I misunderstood your question, and you do want it to scale (i.e. fit on 8.5" x 11" letter paper) simply select "Letter" under the same option mentioned above.