Get PDF Info

Page count and encryption status are the two things you usually want before deciding what to do with a file. Both come off the reader, but the order of the calls matters for encrypted documents, because an encrypted file has no readable page tree until it has been decrypted.

Doing it

f, err := os.Open(inputPath)
if err != nil {
    return err
}
defer f.Close()

pdfReader, err := model.NewPdfReader(f)
if err != nil {
    return err
}

isEncrypted, err := pdfReader.IsEncrypted()
if err != nil {
    return err
}
if isEncrypted {
    auth, err := pdfReader.Decrypt([]byte("")) // or the real password
    if err != nil {
        return err
    }
    if !auth {
        return errors.New("password required")
    }
}

numPages, err := pdfReader.GetNumPages()

model.NewPdfReader is the deliberate choice here. It does not attempt decryption, so it returns successfully for an encrypted file and leaves you to call Decrypt yourself. The other constructors, NewPdfReaderFromFile and NewPdfReaderWithOpts, try the password from ReaderOpts (the empty string by default) and fail outright with “unable to decrypt password protected file” when that does not authenticate. Use those when you already have the password; use NewPdfReader when you want to report on files you cannot open.

Decrypt reloads the document structure on success, which is why GetNumPages comes after it.

Limitations

Calling GetNumPages on an undecrypted encrypted document returns the error “file need to be decrypted first” rather than zero. The same guard sits in front of page access, so there is no way to count pages without authenticating first.

Decrypt returning false means the password was wrong, not that something failed. The error return is reserved for a malformed encryption dictionary. Authenticating with the user password rather than the owner password still opens the file, but the document’s permission flags then apply; CheckAccessRights(password) returns those permissions alongside the viewable flag if you need to tell the two apart, and GetEncryptionMethod() describes the scheme in use.

Neither call says anything about the document’s own metadata. Title, author, producer and creation date live in the information dictionary, reachable through pdfReader.GetPdfInfo(), and the file’s PDF version through pdfReader.PdfVersion(). The metadata guides cover those.

Run the example

getPdfProperties opens each file named on the command line and returns a PdfProperties value holding the page count, the encryption flag, and whether the document is viewable without a password.

git clone https://github.com/unidoc/unipdf-examples.git
cd unipdf-examples/analysis
go run pdf_info.go input1.pdf [input2.pdf] ...

If this is your first time using UniPDF, follow the getting started guide to create an API key and set up your development environment.

Sample output

Input file: templates/documentation/unipdf-templates-documentation.pdf
 Num Pages: 58
 Is Encrypted: false
 Is Viewable (without pass): true