PDF metadata is also encrypted when SetProtection is enabled

[mzakarian]

Description

When setting document metadata (Author, Title, Subject, Creator, Keywords, Producer) using the corresponding Set* methods, the metadata is correctly stored and visible in the generated PDF.

However, as soon as PDF protection is enabled via SetProtection, all metadata except Producer appears encrypted / unreadable in PDF viewers. The Producer field remains as plain text.

This happens even though only printing protection is enabled and no password is set.

Steps to Reproduce

1. Create a minimal Go program using gofpdf:

   package main
   
   import "github.com/phpdave11/gofpdf"
   
   func main() {
       pdf := gofpdf.New("P", "mm", "A4", "")
   
       // Set metadata
       pdf.SetTitle("SetTitle", true)
       pdf.SetAuthor("SetAuthor", true)
       pdf.SetSubject("SetSubject", true)
       pdf.SetCreator("SetCreator", true)
       pdf.SetKeywords("SetKeywords", true)
       pdf.SetProducer("SetProducer", true)
   
       pdf.AddPage()
       pdf.SetFont("Arial", "", 12)
       pdf.Cell(40, 10, "Hello, world")
   
       // Case 1: without protection
       if err := pdf.OutputFileAndClose("no_protection.pdf"); err != nil {
           panic(err)
       }
   
       // Case 2: with protection
       pdf = gofpdf.New("P", "mm", "A4", "")
       pdf.SetTitle("SetTitle", true)
       pdf.SetAuthor("SetAuthor", true)
       pdf.SetSubject("SetSubject", true)
       pdf.SetCreator("SetCreator", true)
       pdf.SetKeywords("SetKeywords", true)
       pdf.SetProducer("SetProducer", true)
   
       pdf.AddPage()
       pdf.SetFont("Arial", "", 12)
       pdf.Cell(40, 10, "Hello, world")
   
       // Enable protection (printing only, no passwords)
       pdf.SetProtection(gofpdf.CnProtectPrint, "", "")
   
       if err := pdf.OutputFileAndClose("with_protection.pdf"); err != nil {
           panic(err)
       }
   }

2. Open both no_protection.pdf and with_protection.pdf in a PDF viewer.

3. Inspect the document properties / metadata.

Expected Behavior

All metadata fields (Title, Author, Subject, Creator, Keywords, Producer) should remain readable and unchanged when enabling protection with SetProtection, since only permissions are being modified.

Actual Behavior

• In no_protection.pdf, all metadata fields are displayed correctly as set:
  • Title: SetTitle
  • Author: SetAuthor
  • Subject: SetSubject
  • Creator: SetCreator
  • Keywords: SetKeywords
  • Producer: SetProducer
• In with_protection.pdf, the following fields appear encrypted / unreadable:
  • Title
  • Author
  • Subject
  • Creator
  • Keywords
• Only the Producer field still appears as plain text (SetProducer).

Environment

• gofpdf version: v1.4.3
• Go version: go1.25.3
• OS: (macOS 26.1 Tahoe)
• PDF viewer(s) tested: Adobe Acrobat Reader DC, Apple Preview