I have been hitting pdf Arranger pretty hard splitting A3 scans of Model Engineer magazines back into page order. It does the job effortlessly and being able to see the whole mag at once allows me to check if any pages need rescanning. The problem I hit though is trying to merge two A4 pages back to one, where I get the above message. pip install gives me a pikepdf of 9.3.0 so well above '3' ... so what am I missing?