I am afraid that I will lose my data if I convert a Deal to a Project. What should I do?

The best way to save your data during conversion is through field mapping.
Vtiger CRM helps you map custom fields of Deals to Projects. So when you convert a deal to a project,

• the CRM will consider the field mapping, and 
• transfers the field values in Deals to the selected target fields in Projects.

To know more about Deal to Project Mapping, click here.