LibreOffice

LibreOffice is a useful office suite that is compatible with Microsoft Office as well as others such as OpenOffice and others. It includes Writer (word processing), Calc (spreadsheets), Impress (presentations), Draw (vector graphics and flowcharts), Base (databases) and Math (formula editing). There is also export to .PDF, and lots of templates and functions.

LibreOffice is based on the OpenOffice project, where its development has taken a different direction from OpenOffice, so you will find different features although the packages are very similar.

LibreOffice offers the best compatibility of any office suite, from native support for Open Document Format (ODF), which uses more advanced security and interoperability features than proprietary formats, to near 100% support for DOCX, XLSX and PPTX files. In addition, LibreOffice includes filters for a large number of previously used document formats, making it the best you can get in terms of interoperability today.

If you need help with LibreOffice, there are English tutorials and guides at https://cs.libreoffice.org/get-help/documentation/ and plenty of tutorial and help videos on YouTube.