How (language / lib) to modify the finished excel file on the server side?

Question

Automation

There are ready-made xlsx files - declarations, quite complex in format: fonts, formatting, embedded images. It is necessary to automate the filling.
I looked at the libraries for my favorite nodejs and did not find a complete solution. There are either parsers that turn a document into an object and writers that write an object to a file. Needless to say, these objects are not compatible :) - this is the time, i.e. you can’t just parse it and write it down, and two - parsing is very limited and you can forget about formatting and images.
Language - any server. nodejs, php, python, etc. also hardcore c/c++

Answer 1

xlsx, docx can be processed through php, these are XML files
You can manually XMLReader + SIMpleXML
You can search for a ready-made class for example PHPExel but either smart ...

Answer 2

phpExcel will help, but a) eats up a lot of memory b) formatting can "break" for complex files. We worked quite successfully with phpExcel with files up to 6000 lines, then the time / memory consumption problems began.
If the server is under Windows, you can try to dig around www.php.net/manual/en/refs.utilspec.windows.php .