在我看来，就像addAttachment-Method始终替换了当前附件一样。

来自PyPDF2 Github中的pdf.py：

def addAttachment(self,fname,fdata):
    file_entry = DecodedStreamObject()
    file_entry.setData(fdata)
    file_entry.update({
            NameObject("/Type"): NameObject("/EmbeddedFile")
            })

    efEntry = DictionaryObject()
    efEntry.update({ NameObject("/F"):file_entry })

    filespec = DictionaryObject()
    filespec.update({
            NameObject("/Type"): NameObject("/Filespec"),NameObject("/F"): createStringObject(fname),# Perhaps also try TextStringObject
            NameObject("/EF"): efEntry
            })

    embeddedFilesNamesDictionary = DictionaryObject()
    embeddedFilesNamesDictionary.update({
            NameObject("/Names"): ArrayObject([createStringObject(fname),filespec])
            })

    embeddedFilesDictionary = DictionaryObject()
    embeddedFilesDictionary.update({
            NameObject("/EmbeddedFiles"): embeddedFilesNamesDictionary
            })
    # Update the root
    self._root_object.update({
        NameObject("/Names"): embeddedFilesDictionary
        })

我相信的地方

self._root_object.update({
        NameObject("/Names"): embeddedFilesDictionary
        })

替换附件，而不是添加附件。

编辑： 这个脚本对我来说可以附加两个.txt文件。 它使用了上面的addAttachment方法，我对该方法进行了一些调整，以允许附加多个文件。

from PyPDF2 import PdfFileReader,PdfFileWriter
from PyPDF2.generic import DecodedStreamObject,NameObject,DictionaryObject,createStringObject,ArrayObject


def appendAttachment(myPdfFileWriterObj,fdata):
    # The entry for the file
    file_entry = DecodedStreamObject()
    file_entry.setData(fdata)
    file_entry.update({NameObject("/Type"): NameObject("/EmbeddedFile")})

    # The Filespec entry
    efEntry = DictionaryObject()
    efEntry.update({ NameObject("/F"):file_entry })

    filespec = DictionaryObject()
    filespec.update({NameObject("/Type"): NameObject("/Filespec"),NameObject("/EF"): efEntry})

    if "/Names" not in myPdfFileWriterObj._root_object.keys():
        # No files attached yet. Create the entry for the root,as it needs a reference to the Filespec
        embeddedFilesNamesDictionary = DictionaryObject()
        embeddedFilesNamesDictionary.update({NameObject("/Names"): ArrayObject([createStringObject(fname),filespec])})

        embeddedFilesDictionary = DictionaryObject()
        embeddedFilesDictionary.update({NameObject("/EmbeddedFiles"): embeddedFilesNamesDictionary})
        myPdfFileWriterObj._root_object.update({NameObject("/Names"): embeddedFilesDictionary})
    else:
        # There are files already attached. Append the new file.
        myPdfFileWriterObj._root_object["/Names"]["/EmbeddedFiles"]["/Names"].append(createStringObject(fname))
        myPdfFileWriterObj._root_object["/Names"]["/EmbeddedFiles"]["/Names"].append(filespec)


fr = PdfFileReader('dummy.pdf','rb')
fw = PdfFileWriter()
fw.appendPagesFromReader(fr)

my_attach_files = ['test.txt','test2.txt']
for my_test in my_attach_files:
    with open(my_test,'rb') as my_test_attachment:
        my_test_data = my_test_attachment.read()
    appendAttachment(fw,my_test,my_test_data)

with open('dummy_new.pdf','wb') as file:
    fw.write(file)

希望这对您有用。