How to Lock Adobe Acrobat PDF Files
Many people distribute important files over the Internet in PDF format. Bloggers and marketers sell ebooks as PDFs because the software to read PDFs is free and they can prevent others from changing and copying the text. Adobe Acrobat allows the PDF creator to lock, or restrict the permission levels, of the document.
Open the PDF you want to lock in Adobe Acrobat.
Select "Properties" from the "File" menu. Click on the "Security" tab.
Click "Yes" if prompted.
Select a compatibility level from the drop-down menu. This will determine the encryption level of the PDF document. A file encrypted to Adobe Reader 9 standard will not work in Adobe Reader 3. Choose the earliest version of the software that you want people to use to read the PDF. Remember, Adobe Reader can be updated free if the reader has an earlier version than you allow.
Choose what document components to encrypt, or lock. You can lock all of the document contents, only file attachments or everything but the metadata.
Select the type of password to lock the PDF. You can opt to require a password to open the PDF or require a password to edit the PDF. Type the password into the designated field.
Click "Enable Copying of Text, Images, and Other Content" if you want to allow copying and pasting of the PDF contents into other documents.
Click "OK" and confirm the password.