How to Secure a PDF using Adobe Acrobat DC
1). Open the PDF document that you would like to password protect.
2) Click View>Tools>Protect>Open (See below screenshot)
3) On the toolbar click Encrypt>Encrypt with Password. (See below screenshot)
4) In the Password Security window, place a check mark next to ‘Require a password to open the document’. (See below screenshot covering steps 4 and 5)
5) In the blank field next to ‘Document Open Password’ insert the password you would like to use to protect the PDF, then click OK. (See below screenshot covering steps 4 and 5)
6) After clicking OK, the below box will appear asking you to re-enter the document password. Re-enter the document password and click OK.
7) From step 6 after clicking OK the following box will appear as a reminder that the password will not be applied to the PDF until the PDF is saved.
8) Close the PDF and you will be prompted with the below prompt to Save changes. Click ‘Yes’.
9) Once you have reached this point you have successfully password protected a PDF. From this point forward each time the PDF is opened the user will need to know the document password in order to open the PDF.