Parse PDF, some content appears garbled

[sh6x-228]

For security reasons, I cannot share the problematic PDF file.
The garbled text originally occurred when using the reader.GetPlainText() method from the demo.
After switching to the following approach:

for i := 1; i <= reader.NumPage(); i++ {
    text, e := reader.Page(i).GetPlainText(nil)
    if e != nil {
        continue
    }

    if _, e = w.Write([]byte(text)); e != nil {
        continue
    }
}

to extract the content page by page, the garbled text issue no longer occurs.