Hi, it seems that the password you mean is owner password which prevents you from editing the pdf file. In this case, you need a password remover like AnyBizSoft pdf password remover. It is very easy to use. After three steps, you can edit it with Acrobat or other pdf editors.
Here's the download link:
http://www.anypdftools.com/pdf-password-remover.html
If you don't have a pdf editor like Acrobat, here I provide you an alternative:
1.convert it to editable word format using a pdf to word converter(Free)
download link:
http://www.anypdftools.com/pdf-to-word.html
2. convert it back to pdf using a pdf creator (eg. Cute pdf writer). Here's a list of them:
http://www.anypdftools.com/free-word-to-pdf-creator.html
Hope it helps.