Do you mean copying from Microsoft to Wordpress or another CMS ? If so i have not tried that, but i dont think you should get errors if you copy dat from Microsoft Word, What version are you using ?
save as a file format other than word. or paste into html and reformat or use a conversion tool Word puts a lot of junk code into everything if you just cut and paste.
Copying from Word sucks ! Better to paste onto notepad first to strip out all the crap and make your modifications within the WP post editor (bolds, colors, tagss and such). That's the safest way, and inevitably the least time consuming.
Paste to notepad first to remove the ms word formating and then copy it from there and paste in wordpress.... format it there!