PDF Merge

Overview

Since v1.0.2

gpdf can merge multiple PDF documents into one. You can combine entire documents or extract specific page ranges from each source.

Common use cases:

Combining a cover page with generated content
Merging invoices into a single bundle
Extracting specific pages from a large document
Assembling reports from multiple sources

Basic Merge

Use gpdf.Merge() to combine two or more PDFs:

import gpdf "github.com/gpdf-dev/gpdf"

cover, _ := os.ReadFile("cover.pdf")
body, _ := os.ReadFile("body.pdf")

merged, err := gpdf.Merge([]gpdf.Source{
    {Data: cover},
    {Data: body},
})
if err != nil {
    log.Fatal(err)
}

os.WriteFile("output.pdf", merged, 0644)

Each Source contains raw PDF bytes. By default, all pages from each source are included.

Page Range Extraction

Use PageRange to include only specific pages from a source (1-based, inclusive):

full, _ := os.ReadFile("report.pdf")

// Extract pages 2 through 4
extracted, err := gpdf.Merge([]gpdf.Source{
    {Data: full, Pages: gpdf.PageRange{From: 2, To: 4}},
})

PageRange rules:

From: 0 or omitted — starts from the first page
To: 0 or omitted — goes through the last page
Zero value PageRange{} — includes all pages

Setting Metadata

Use WithMergeMetadata to set document info on the merged output:

merged, err := gpdf.Merge(
    []gpdf.Source{
        {Data: cover},
        {Data: body},
        {Data: appendix},
    },
    gpdf.WithMergeMetadata("Policy Bundle", "Example Ltd", "gpdf"),
)

Parameters: title, author, producer.

Merge + Overlay

Combine merge with overlay to add page numbers or watermarks after merging:

// Step 1: Merge documents
merged, _ := gpdf.Merge([]gpdf.Source{
    {Data: cover},
    {Data: body},
})

// Step 2: Open merged result and add page numbers
doc, _ := gpdf.Open(merged)
count, _ := doc.PageCount()

doc.EachPage(func(i int, p *template.PageBuilder) {
    p.Absolute(document.Mm(170), document.Mm(285), func(c *template.ColBuilder) {
        c.Text(fmt.Sprintf("%d / %d", i+1, count),
            template.FontSize(10),
            template.AlignRight(),
        )
    }, template.AbsoluteWidth(document.Mm(20)))
})

result, _ := doc.Save()
os.WriteFile("final.pdf", result, 0644)

API Reference

Function / Type	Description
`gpdf.Merge(sources, opts...)`	Merge multiple PDFs into one
`gpdf.Source`	Input PDF: `Data []byte` + `Pages PageRange`
`gpdf.PageRange`	1-based inclusive range: `From`, `To` (0 = default)
`gpdf.WithMergeMetadata(title, author, producer)`	Set document metadata on output

Next Steps

Existing PDF Overlay — Add content on top of existing PDFs
Examples: Merge — More merge code examples
API Reference — Full gpdf package reference