PDF privacy and security

Most of this subject is about the gap between what a feature looks like it does and what it actually does. A black rectangle is not redaction, and a picture of a signature is not a signature.

Are browser-based PDF tools really private?Are browser-based PDF tools actually private, or do they still upload my file somewhere?Browser-based PDF tools can process a file without uploading it. Here is how that works on iBuildPDF, and how to verify it yourself.
What personal information is hidden in a PDFWhat personal information is hidden inside a PDF, and how do I remove it?Every PDF carries author, software and timestamp fields you never typed. Here is what is in there, how to read it, and how to strip it.
How to redact a PDF so the text cannot be recoveredHow do I black out text in a PDF so it genuinely cannot be recovered?Drawing a black box over text does not delete it. Here is why that fails, what real redaction requires, and how to check your result.
What a PDF password actually protectsWhat does a PDF password actually protect?PDFs have two kinds of password and only one of them encrypts anything. What each protects, what permissions really do, and when a password is the wrong tool.
How to sign a PDFWhat does it mean to sign a PDF?An image of a signature and a cryptographic signature are different things with different legal weight. Which one you need, and how to add it.
How to watermark a PDFDoes a watermark protect my document?What a watermark is good for, what it cannot prevent, and how to add one that is readable without wrecking the document underneath.
How to password protect a PDFHow do I put a password on a PDF?PDFs take two different passwords and only one of them keeps people out. Which to use, and what each is worth.
Are free online PDF tools safe?Is it safe to use a free online PDF tool?It depends entirely on whether your file is uploaded. How to tell the difference in about ten seconds, before you choose a file.
Can a PDF contain a virus?Is it safe to open a PDF I was not expecting?A PDF can carry scripts, an action that runs on opening, and other files inside it. Most harm comes from neither. What to check before you open one.
What a PDF tool can see in your Google DriveIf I let a PDF site open a file from my Google Drive, what else can it see?Google has three levels of Drive access and the difference is enormous. What a site asked for is on the permission screen, if you know what to read.

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