What Is an NDA?
NDA is a non-disclosure agreement that is concluded to protect confidential information, such as financial terms of the contract, private data, or intellectual property. It is often either large companies or startups that conclude NDAs with designers.
Read the Terms And Conditions Carefully
If you're asked to sign an NDA, read the entire document. After signing an NDA, designers are often not allowed to show their work and speak about it until the project is finished. Restrictions can be more severe, such as a complete ban on posting the work in the portfolio.
In that case, try to negotiate milder terms, such as the possibility of publishing your work with the client's permission, or 1 year after the project is finalized. Only sign the document when both you and your client are happy with it.
Ask If Something Is Unclear
If you don't understand the terms, ask to clarify them or contact a lawyer. Keep in mind that if you violate the NDA, you may have to pay financial damages for disclosing the information.
If You Aren't Allowed To Add the Project To Your Portfolio...
...it's worth increasing its price as the portfolio is one of your main tools for finding new orders.