You don't necessarily need a paid program if you can't open a compressed file received via email or want to combine multiple files into one to send. The free open-source compression program 7-Zip is sufficient.
What is 7-Zip? 7-Zip is a free, open-source file compression and decompression program. Its proprietary 7z format is known for its high compression ratio, and it can also create and decompress common formats such as ZIP, TAR, and GZIP. It is free for both personal and commercial use, and requires no registration or payment.
It is good to use in situations like this. - When you want to combine multiple photos or documents into a single file - When you need to extract a received ZIP or 7z file - When you want to reduce a large file size to avoid hitting email attachment limits
Basic usage 1. Download and install the version suitable for your computer (mostly 64-bit Windows) from the official website (7-zip.org). 2. Select the files to compress, right-click → 7-Zip → select 'Add to archive'. 3. To extract, right-click on the compressed file → 7-Zip → select 'Extract here'.
Points to note - Password-protected compressed files can only be extracted if you know the password. Do not open compressed files sent by strangers indiscriminately. Malicious software may be hidden within. - Since the official version of 7-Zip on Mac is for the terminal (console), it is a good idea to know about free compression apps for Mac like Keka if you want to use it comfortably with a mouse. It is safer to obtain it from the official site rather than from a site with an unclear source.
Source: 7-Zip Official Download Page (https://www.7-zip.org/download.html) and 7-Zip guide (https://www.7-zip.org/links.html)를 I organized this based on your reference. | 
