No add to cart - product catalog Features
Remove Cart links from header
Remove Add to cart button from product page
Remove Add to cart button from category grid view page
Remove Add to cart button from category list view page
Remove Add to cart button from product compare
Remove Add to cart button from wishlists
Remove Add to cart button from search results
Remove Add to cart button from Module - Specials
Remove Add to cart button from Module - Bestseller
Remove Add to cart button from Module - Latest
Remove Add to cart button from Module - Featured


The second module included in this pack.

No add to cart if product price = 0.00 Features
Remove Add to cart button from product page if product price = 0.00
Remove Add to cart button from category grid view page if product price = 0.00
Remove Add to cart button from category list view page if product price = 0.00
For OpenCart 2.0 only
Remove Price if it is 0.00 from category list view page if product price = 0.00
Remove Price if it is 0.00 from product page if product price = 0.00
Serverside check if added product price is = 0.00 it won't be added to cart. (Even if someone tricks the front-end and makes a POST ajax request.)

DEMO
http://ggwshop.com/ocart2031noaddtocart/index.php?route=product/category&path=18

(?) How to install - Product catalog
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for OpenCart 2.0.x
FILE: ggw_product_catalog20.xml
1 - Requires vQmod 2.4+
2 - Upload to SITE_ROOT / vqmod / xml

SUPPORT e-mail in mod's author field.
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If you need support - send FTP and admin login details with few lines descriptions of the problem and we will fix it.