A PDF file may be encrypted for security, or digitally signed for authentication.

The standard security provided by Acrobat PDF consists of two different methods and two different passwords, user password, which encrypts the file and prevents opening, and owner password, which specifies operations that should be restricted even when the document is decrypted, which can include: printing, copying text and graphics out of the document, modifying the document, or adding or modifying text notes and AcroForm fields. The user password encrypts the file and requires password cracking to defeat, with difficulty depending on password strength and encryption method. The owner password does not encrypt the file, and instead relies on client software to respect these restrictions, and is not secure. An "owner password" can be removed by many commonly available "PDF cracking" software, including some free online services. Thus, the use restrictions that a document author places on a PDF document are not secure, and cannot be assured once the file is distributed; this warning is displayed when applying such restrictions using Adobe Acrobat software to create or edit PDF files.

You can Secure PDF by our online program, PDFConvert desktop software or command line program.

Encrypt PDF Form
Local PDF File:
User Password:
Owner Password:
PDF Restrictions:	Allows to print PDF with high quality Allows to print PDF with low quality Allows to modify PDF contents Allows to copy PDF contents Allows to edit PDF annotations and fill PDF forms

Use this form to encrypt a PDF file with user/owner password and set PDF restrictions.

1. Click the "Choose File" button (different web browsers may have different button names such as "browse..."), a browse window will open, select a local Adobe PDF file and click the "Open" button.
2. Enter a user password if you want this PDF needs password to open. Enter an owner password if you want to set restrictions. Choose PDF restrictions from list.
3. Click the "Encrypt Now!" button to convert. Wait a few seconds for the task to finish.
4. You can download or view the output PDF file on your web browser after conversion.

After installing PDFConvert software, click Start - Programs - PDFConvert - PDFConvert to run.

Click Toolbar Settings, Click the "PDF Security" button on the left.

Select Enabled Password Encryption checkbox. Enter passwords to open document or passwords to edit document, select PDF restriction options, choose encryption algorithm from 40-bit, 128-bit AES and 128-bit ARC-FOUR. Leaving this page will save settings.

PDFConvert will set password and add restrictions to the PDF file when a PDF file is created from image files or documents.

The password to open PDF is called user password. The user password encrypts the PDF file and requires password cracking to defeat, with difficulty depending on password strength and encryption method. It is potentially very secure. The password to set PDF restrictions is called owner password. The owner password does not encrypt the file, and instead relies on client software to respect these restrictions, and is not secure.

Download pdfconvert.exe, and run pdfconvert.exe command line program to Secure PDF on background without windows showed.

/?

Shows all command line parameters of pdfconvert.exe.

/i

input files

For example: pdfconvert.exe /i "c:\pdf\1.pdf"

/o

output folder

For example: pdfconvert.exe /o "c:\pdf2"

/op

Set the PDF file User password

/ep

Set the PDF file Owner password

/edt

Enable copying of text, image and other context (0: can't copy, 1: can copy)

/ept

Enable PDF printing (0: can't print, 1: can print)

/pst

Set the PDF file encryption algorithm (0: 40bit, 1: 128bit AES, 2: 128bit ARC-FOUR)

For example: This command will add user password "abcdef", owner password "123456" and restrictions to local PDF file "c:\pdf\1.pdf", and save file to "c:\pdf2\1.pdf".
pdfconvert.exe /i "c:\pdf\1.pdf" /o "c:\pdf2" /op abcdef /ep 123456 /edt 0 /ept 0