What technologies are used to compress/convert?

Question

Data compression

There are many different sites that compress, convert and something else online ...
What technologies are / are used for this?
Can I do something of my own in some language, such as Python, PHP? For your personal use.
For example, converting secret documents through any service is not very comme il faut, I would like to do it myself. Without installing any software. Something like a local site with such functionality.

Answer 1

Data compression algorithms do not depend on the implementation in the programming language used. And also don't confuse data compression with data encryption. Compressed data can be recovered by knowing the compression algorithm, while encrypted data can be recovered only if the decryption key is available.