如何在 Android 上创建受密码保护的 PDF 的可编辑副本？

Question

Context

I'm using a third-party library called PsPdfKit to edit PDF files, adding annotations - like PNG images, and text decorations - on top of the PDF document. But there's a limitation of this library where I'm not able to use this annotation feature on password-protected PDF files. I can open and see the documents, but I'm unable to actually drop these annotations in. What I'm trying to do now is to figure out whether could be possible to create an editable copy of the PDF file.

Question

Is there any way on Android to create an editable copy of a password protected PDF file? Again, these password protected PDF files are only preventing writing any changes on top of the PDF, you don't actually need a password to see the PDF content.

My idea is to create an editable copy of the PDF file and then pass that copy to the PsPdfKit library.

Answer 1

Okay, so I've finally figured out a workaround for this issue. What I did was to instantiate the password protected PDF file via PsPdfKit and then create a writeable copy of the file using the page bitmaps of the password protected file. A bit of a hacky solution, but it did allow me to use the annotation feature.

// We open the password-protected file.
val readOnlyPdfDocument = PdfDocumentLoader.openDocument(applicationContext, readOnlyFile.toUri())
// Use the PsPdfKit API to create a copy of the pages of this document
val task = PdfProcessorTask.newPage(NewPage.fromPage(readOnlyPdfDocument, 0).backgroundColor(Color.RED).build())
for (i in 1 until readOnlyPdfDocument.pageCount) {
   task.addNewPage(NewPage.fromPage(readOnlyPdfDocument, i).backgroundColor(Color.RED).build(), i)
}
// Finally store the writeable PDF document in a new file
val writeableFile = File(applicationContext.cacheDir, "Writeable.pdf")
PdfProcessor.processDocument(task, writeableFile)