Add watermark to public trust center documents

Signed-off-by: Sacha Al Himdani <sacha@getprobo.com>

pkg/watermarkpdf/watermarkpdf.go

@@ -0,0 +1,58 @@
+// Copyright (c) 2025 Probo Inc <hello@getprobo.com>.
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+// AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+// OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+// PERFORMANCE OF THIS SOFTWARE.
+
+package watermarkpdf
+
+import (
+	"bytes"
+	"fmt"
+	"strings"
+	"time"
+
+	"github.com/pdfcpu/pdfcpu/pkg/api"
+	"github.com/pdfcpu/pdfcpu/pkg/pdfcpu/model"
+)
+
+func AddConfidentialWithTimestamp(pdfData []byte, email string) ([]byte, error) {
+	reader := bytes.NewReader(pdfData)
+	var buf bytes.Buffer
+
+	// Replace email with invisible characters to prevent auto-linking
+	formattedEmail := strings.ReplaceAll(email, "@", "\u200B@\u200B")
+	formattedEmail = strings.ReplaceAll(formattedEmail, ".", "\u200B.\u200B")
+
+	watermarkText := strings.Join([]string{
+		"Confidential",
+		formattedEmail,
+		time.Now().Format("02/01/2006"),
+	}, "\n")
+
+	watermarkConf := model.DefaultWatermarkConfig()
+	watermarkConf.Mode = model.WMText
+	watermarkConf.TextString = watermarkText
+	watermarkConf.FontName = "Helvetica"
+	watermarkConf.FontSize = 120
+	watermarkConf.Rotation = 55
+	watermarkConf.Opacity = 0.20
+	watermarkConf.OnTop = true
+	watermarkConf.ScaleAbs = true
+	watermarkConf.Update = false
+
+	err := api.AddWatermarks(reader, &buf, nil, watermarkConf, nil)
+	if err != nil {
+		return nil, fmt.Errorf("failed to add watermark: %w", err)
+	}
+
+	return buf.Bytes(), nil
+}