Marks made by White-Out and similar products are always visible, and make for unprofessional-looking documents. It is often preferable to blot and scrape documents, which can often remove most if not all of the ink. These techniques only work on documents produced by ink jet printers. Laser printers use slightly different chemicals that can only be removed through scraping techniques. Not all documents can be treated in this fashion, and success depends highly on the quality of the paper used. The thicker the paper, the easier it will be to remove errors.
Lay the document on a flat surface. Dab the ink you want to remove with a cotton swab to soak up any excess ink.
Scrape in a downward motion using the razor blade (toward the bottom of the document). The blade should be held at approximately a 45 degree angle with the blade facing you. Do not scrape too hard or apply direct pressure, or you will damage the paper. Wipe away the ink residue with the cotton swabs.
Repeat steps 3 and 4 until the document has been successfully treated. Often it is better to get most of it then risk damaging the paper by overtreating it with this process.