XML validation

I have a Python code that does the conversion from pdf to xml. So i have 3 different types of pdf's and this code automatically converts them into xml separately and as also in one unique xml output that there are all the files inside.. But there are some problems in the contents of some tags which is not matching with the universal xml format, so it creates problems when that xml file is converted to other formats such as json in other platforms.. Some filtration and regex techniques should be applied and at the end the xml outputs should be valid. I need help from who is good at Python and XML formats.