Adding a text watermark in Go with Go-Resty

In this guide, we'll walk you through the process of adding text watermarks to your PDF files, using PDFShift's API.

Adding a watermark to your PDF can be done by adding the watermark object to your query. Adding a text allows you to customize its content and PDFShift's API provides a few properties to help you customize the visual aspect, such as the font size, color, and position.

package main

import (
    "encoding/base64"
    "encoding/json"
    "fmt"
    "io/ioutil"
    "github.com/go-resty/resty/v2"
)

func main() {
    // You can get an API key at https://pdfshift.io
    apiKey := "sk_xxxxxxxxxxxx"

    params := map[string]interface{}{
        "source": "https://www.example.com",
        "watermark": map[string]string{
            "text":       "PROTECTED DOCUMENT",
            "offset_x":   "center",
            "offset_top": "top",
        },
    }

    // Marshal the parameters into JSON
    jsonParams, err := json.Marshal(params)
    if err != nil {
        fmt.Println("Error marshaling JSON:", err)
        return
    }
    // Create a new Resty client
    client := resty.New()

    // Perform the request
    resp, err := client.R().
        SetHeader("Content-Type", "application/json").
        SetBasicAuth("api", apiKey).
        SetBody(jsonParams).
        Post("https://api.pdfshift.io/v3/convert/pdf")

    if err != nil {
        fmt.Println("Error performing request:", err)
        return
    }

    // Check response status code
    if resp.StatusCode() >= 400 {
        fmt.Printf("Request failed with status code %d: %s\n", resp.StatusCode(), string(resp.Body()))
        return
    }

    // Save the PDF document
    err = ioutil.WriteFile("result.pdf", resp.Body(), 0644)
    if err != nil {
        fmt.Println("Error saving PDF document:", err)
        return
    }

    fmt.Println("The PDF document was generated and saved to result.pdf")
}

You can customize the text watermark by applying the following properties:

font_size: The size of the text. An integer value in pixels. Defaults to 16.
font_family : The font family to be used. Defaults to Helvetica.
font_color : The color of the text. A hexadecimal color value. Defaults to '000000'.
font_opacity : The opacity of the text. A float value between 0 and 100. Defaults to 100.
font_bold: A boolean to set the text as bold. Defaults to false.
font_italic: A boolean to set the text as italic. Defaults to false.

You can also customize the position of the text watermark by applying the following properties:

offset_x: The horizontal position of the text. Can be 'left', 'center', 'right', or a specific value in pixels. Defaults to 'center'.
offset_y: The vertical position of the text. Can be 'top', 'middle', 'bottom', or a specific value in pixels. Defaults to 'center'.

For the offset positions, we accept a value in integer which will be translated to pixels, but you can also pass a unit such as 'px', 'in', 'cm', 'mm', 'pt'.

For example:

params = {
    "source": "https://www.example.com",
    "watermark": {
        "text": "PROTECTED DOCUMENT",
        "offset_x": "5cm",
        "offset_top": "15mm"
    }
}

For further details on the watermark property and its usage, please refer to our dedicated documentation.

We hope this guide was helpful. If you have any questions or noticed any issues on the code above,
feel free to drop us a line.