Mac update

Ask Apple if your machine can be upgraded to Catalina.

https://www.apple.com/macos/how-to-upgrade/

For HTML, CSS and JavaScript, you need a code editor that's compatible with your Mac.

Brackets and VS Code are free. 

• http://brackets.io/
• https://code.visualstudio.com/#alt-downloads

Visual editors like Dreamweaver, Pinegrow and Wappler cost money.  

• https://www.adobe.com/products/dreamweaver.html
• https://pinegrow.com/
• https://wappler.io/

This clearly has nothing to do with use of Acrobat Reader. Moving to a more appropriate community.