I use PdfFileMerger from PyPDF2 in a plugin that I want to migrate from qgis 2 to 3 but it seems that this lib doesn't exist in qgis 3 (python 3.6).
How I can do this?
Install PyPDF2 using pip.
python -m pip install PyPDF2
Remember that you need set python interpreter for use qgis 3 (python 3.6) https://gis.stackexchange.com/a/268606/49538
And fro using it:
from PyPDF2 import PdfFileReader