How to Password Protect a PDF

This How.com.vn teaches you how to lock a PDF with a password, making it impossible to open without entering the password in question. There are a couple of free online services that you can use to do this, or you can use the paid version of Adobe Acrobat Pro if you have it.

Method 1

Method 1 of 3:

Using SmallPDF

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1
Open SmallPDF's protection page. Go to https://smallpdf.com/protect-pdf in your web browser. SmallPDF will allow you to apply a password to your PDF, making it impossible to open without knowing the password.
- If you want to lock the option of editing the PDF with a password, try using PDF2Go instead.
It's a link in the red box that's in the middle of the page. A window will open.
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Go to the location of the PDF that you want to password-protect, then click the PDF in question.
It's in the bottom-right corner of the window. Your PDF will be uploaded to the SmallPDF website.
5
Enter a password. Type the password that you want to use into the "Choose your password" text field, then re-enter the password in the "Repeat your password" text field below it.
- Your passwords must match each other in order for you to be able to continue.
It's a red button below the password text fields. Doing so will apply your password to your PDF.
This button appears on the left side of the page once your PDF's password has been applied. Doing so will download the password-protected PDF onto your computer. From now on, whenever you want to open this PDF, you'll need to enter the password that you set.

Method 2

Method 2 of 3:

Using PDF2Go

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Go to https://www.pdf2go.com/protect-pdf in your web browser. Like SmallPDF, PDF2Go allows you to protect the PDF from being opened without a password; however, it also allows you to lock the PDF for editing, meaning no one will be able to change the PDF without knowing both passwords.
It's near the top of the page. A window will open.
Go to the PDF to which you want to add a password, then click it to select it.
It's in the bottom-right corner of the window. This will prompt the PDF to upload to the website.
This section is in the middle of the page. You'll set the password here.
Type your PDF's password into the "Enter user's password" text box, then repeat the password in the "Repeat user's password" text box below it. This is the password that you'll use to open the PDF.
Click the No bubbles below the "Allow Printing?", "Allow Copying?", and "Allow Modification?" headings.
Type the password that you want to use for the PDF's editing lock into the "Enter owner's password" and "Repeat owner's password" text boxes near the bottom of the page.
It's a green button at the bottom of the page. Doing so will prompt PDF2Go to begin assigning the passwords to your PDF.
10
Click Download File. This light-green button is in the upper-right side of the page. The password-protected PDF will download onto your computer. Whenever you want to open or edit the PDF, you'll need to enter the appropriate password(s) first.
- You can also click Download ZIP File in the middle of the page if you want to download the PDF in a compressed (zipped) folder. This may be your only option for particularly large PDFs.

Method 3

Method 3 of 3:

Using Adobe Acrobat Pro

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You cannot edit PDFs (which includes adding passwords to them) if you're using the free Adobe Reader.
Click File in the upper-left corner, click Open... in the resulting drop-down menu, select your PDF, and click Open in the bottom-right corner of the window.
This menu item is at the top of the Adobe Acrobat window (Windows) or the screen (Mac). A drop-down menu will appear.
It's in the drop-down menu. A pop-out menu with additional options will appear.
You'll see this in the pop-out menu. Doing so prompts another pop-out menu.
It's in the final pop-out menu. This will open the "Protect" tool's window.
You'll find this in the middle of the window.^{[1]XResearch source}
Doing so will open the encryption options page.
It's below the "Document Open" heading. This prompts the password text field to become available.
Type the password that you want to use into the "Document Open Password" text field.
Click the "Compatibility" drop-down box, then click the minimum version of Adobe Acrobat with which you want the file to be compatible.
It's in the "Options" section. This will prevent someone from being able to extract select information from the PDF.
It's at the bottom of the page.
Type back in the document's password, then click OK. This will confirm your changes and apply the password to the PDF. You'll now need to enter this password whenever you want to view the PDF.

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Tips

When coming up with a password for your PDF, use the same rules that you'd generally apply to an email or computer password. This will help secure your PDF against lucky or informed guesses.
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Warnings

It is possible to open a locked PDF by using special software. Even if your PDF is password-protected, you should keep it stored in a secure, private location.
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