How to Load a Document in Go

Aspose.PDF FOSS for Go loads a PDF from a file path, an io.Reader, or either source protected by a password, always returning a *Document value to operate on. The library is a Go module installed with go get.

Step-by-Step Guide

Step 1: Install the Package

Add the module to your project:

go get github.com/aspose-pdf-foss/aspose-pdf-foss-for-go

Verify the module resolves:

import asposepdf "github.com/aspose-pdf-foss/aspose-pdf-foss-for-go"

Step 2: Import Required Classes

import (
	pdf "github.com/aspose-pdf-foss/aspose-pdf-foss-for-go"
)

Step 3: Load a PDF from a File Path

pdf.Open loads a PDF file and returns a *Document and an error:

doc, err := pdf.Open("testdata/4pages.pdf")
if err != nil {
	panic(err)
}
fmt.Println(doc.PageCount(), "pages")

Step 4: Load a Password-Protected PDF

pdf.OpenWithPassword opens a file that is encrypted with a user password:

doc, err := pdf.OpenWithPassword("locked.pdf", "secret")
if err != nil {
	panic(err)
}
fmt.Println("opened:", doc.PageCount(), "pages")

Step 5: Load a PDF from a Stream

pdf.OpenStream reads a PDF from any io.Reader — a network response, an in-memory buffer, or a file opened separately. pdf.OpenStreamWithPassword is the password-protected equivalent for streams:

f, err := os.Open("input.pdf")
if err != nil {
	panic(err)
}
defer f.Close()

doc, err := pdf.OpenStream(f)
if err != nil {
	panic(err)
}
fmt.Println(doc.PageCount(), "pages")

// For an encrypted stream, open a separate reader and pass a password:
f2, _ := os.Open("locked.pdf")
defer f2.Close()
doc2, err := pdf.OpenStreamWithPassword(f2, "secret")
if err != nil {
	panic(err)
}
fmt.Println(doc2.PageCount(), "pages (encrypted)")

Step 6: Inspect the Loaded Document

Once loaded, Document.PageCount reports the total number of pages and Document.Page(n) retrieves a single page by its 1-based index:

doc, err := pdf.Open("testdata/4pages.pdf")
if err != nil {
	panic(err)
}
fmt.Printf("Page count: %d\n", doc.PageCount())

page, err := doc.Page(1)
if err != nil {
	panic(err)
}
size, err := page.Size()
if err != nil {
	panic(err)
}
fmt.Printf("Page 1 size: %.0f x %.0f pt\n", size.Width, size.Height)

Common Issues and Fixes

OpenWithPassword still fails after I enter what I believe is the correct password

Providing an incorrect password to OpenWithPassword results in a non-nil error. Passwords are case-sensitive — confirm the exact user password set on the source PDF.

OpenStream returns an error on an encrypted PDF

OpenStream cannot open encrypted PDFs. Use OpenStreamWithPassword for password-protected streams instead.

Do I need OpenWithPassword for a PDF that turns out not to be encrypted?

No — opening an unencrypted file through OpenWithPassword is allowed and behaves the same as a plain Open call, so it is safe to use OpenWithPassword when you are not certain a file is encrypted.

Document.Page(n) returns an error after a successful Open

The page number is out of range. Page uses a 1-based index between 1 and Document.PageCount(); call PageCount() first to validate the range.

Frequently Asked Questions

What file formats can I load with `Open`?

Open, OpenWithPassword, OpenStream, and OpenStreamWithPassword all accept PDF input exclusively.

How do I load a PDF that is already in memory instead of on disk?

Wrap the byte slice in a bytes.Reader (which satisfies io.Reader) and pass it to pdf.OpenStream, or pdf.OpenStreamWithPassword if the bytes represent an encrypted PDF.

How do I load a password-protected PDF?

Call pdf.OpenWithPassword(path, password) for a file path, or pdf.OpenStreamWithPassword(r, password) for a stream.

How do I check how many pages were loaded?

Call Document.PageCount() on the returned *Document.