Update README.md

README.md

+# Introduction, Context
+
 If PDF files are edited with inkscape, or generated with matplotlib, it is a 
 typical scenario that PageGroups are part of those files. If multiple such 
 PDFs are included, e.g. in latex. Only one of those PageGroups is used (there 
-can only be one at least per page). It is not clear if this is a misbehaviour 
+can only be one at least per page). It is not very clear to me if this is a misbehaviour 
 of inkscape, latex or just a general problem in working with both of them. 
 
-Latex will produce warnings/errors in such cases pointing to the PageGroups.
+However, latex will produce warnings/errors in such cases pointing to the PageGroups.
 
 With this script here, PDF files can be edited automatically to remove 
 PageGroups. The internal structure of the PDFs is kept consistent, if needed
-the xref tables are updated and fixed. 
+the xref tables are updated and fixed. The quality of the PDF is not affected. 
+Also the size of the files is not affected (they become a few bytes shorter). 
 
-Use this tool with great care, do not trust its output blindly. Make sure the
-generated files are completely OK for the purpose they are indendet for. 
+This tool helped me to write and review papers for the CMS Collaboration 
+where no errors on latex are allowed in the final step. 
+
+# Warning  
+**Use this tool with great care, do not trust its output blindly**. 
+Make sure image-by-image that the
+generated files are completely OK for the purpose they are indended for! 
 
 I tested this on files editor with inkscape and generated by matplotlib with 
 excellent results. Thus a workflow for files, where the normal application of
 the script does not result in good results, it is worth trying to first import
 in inkscape, re-export as pdf, the apply this script, check output. 
 
-This tool helped me to write and review papers for the CMS Collaboration 
-where no errors on latex are allowed in the final step. 
+Note, this only works on single-page PDFs! It is only intended for individual
+plots/images. 
+
+# Usage
+
+`./strip_pdf.py <file.pdf>`
+
+The script will check if file.pdf has any PageGroups and only if one is found
+it will create a security copy `file.save.pdf` and modify the original file
+to remove the PageGroup. 
+
 
 Ralf Ulrich
 May 2020