Itext7 cleanup method throws error - Index was out of range - pdf

Question

I am getting the below error while trying to redact pdf document using itext7
I am calling pdfCleanupTool.cleanup() method for redaction and sometimes I am getting the below error from the cleanup method:
Index was out of range. Must be non-negative and less than the size of the collection.\r\nParameter name: index
Any help appreciated.
Thanks!
Updates:
Error Log:

Answer 1

There is a bug in the iText 7 PdfTextArray class which generates stack traces like yours. As you don't share your PDF, though, I cannot be sure whether that's the bug bothering you currently.
The Bug
The bug can be provoked quite easily, in Java like this
PdfTextArray textArray = new PdfTextArray();
textArray.add(1);
textArray.add(-1);
textArray.add(1);
(CancelingAdjustments test testCancelingAdjustments)
and similarly in C#.
This essentially may be what happens in the OP's case; redaction involves removal of text pieces from such text arrays and replacement by equivalent numeric adjustments, so such situations may be more probable during redaction than in general.
The Cause
When adding multiple numbers to a PdfTextArray, it attempts to combine them to a single number, and if that single number is zero, remove it altogether:
public boolean add(float number) {
// adding zero doesn't modify the TextArray at all
if (number != 0) {
if (!Float.isNaN(lastNumber)) {
lastNumber = number + lastNumber;
if (lastNumber != 0) {
set(size() - 1, new PdfNumber(lastNumber));
} else {
remove(size() - 1);
}
} else {
lastNumber = number;
super.add(new PdfNumber(lastNumber));
}
lastString = null;
return true;
}
return false;
}
(PdfTextArray method add)
But this code forgets to reset the lastNumber variable to "not a number" after removal due to cancelation. Thus, this bug can be fixed like this:
public boolean add(float number) {
// adding zero doesn't modify the TextArray at all
if (number != 0) {
if (!Float.isNaN(lastNumber)) {
lastNumber = number + lastNumber;
if (lastNumber != 0) {
set(size() - 1, new PdfNumber(lastNumber));
} else {
remove(size() - 1);
lastNumber = Float.NaN;
}
} else {
lastNumber = number;
super.add(new PdfNumber(lastNumber));
}
lastString = null;
return true;
}
return false;
}
(One could improve this some more by testing whether there is some string at the now last position of the array and initialize lastString accordingly.)
The iText/.Net code is very similar here.