1a. Harmonized product standard
First, check the list of harmonised standards. You may need to read the actual text of the standards to be sure whether your product falls under the scope of the standard or not. It is not only about the nature of the product but also the intended use which must be in line with the standard. What is a harmonised standard?
If the product is covered by a harmonised standard, the procedure leading to a Declaration of Performance (DoP) must be folowed before the product is placed on the market.
If the product is not covered by a harmonised standard, a DoP cannot be issued. The product is then outside the so called “harmonized area”. Instead, the legislation of every EU country must be checked for any obligations relevant for placing the product on the market of that country.
1b. European Technical Assessment
Alternatively to harmonized standards, the procedure using EADs and ETAs is possible. The procedure (also leading to DoP and CE marking) is voluntary but once initiated, all the rules related to DoP and CE marking are binding for the manufacturer.
In other words, if an ETA (European Technical Assessment) has been issued for the product, the obligations are the same as for products covered by a harmonised standard and a DoP must be issued.
2. The role of the economic operator
One has to make sure what their role is, as described in Construction Products Regulation 305/2011 (CPR). The fact you have a factory does not make you automatically a manufacturer. On the other hand, you can become a manufacturer without having a single machine. Read this article to understand the roles of economic operators.
If you have identified the obligation to issue a DoP according to point 1, it must be done by the manufacturer. If you are a distributor or another economic operator, you must not issue a DoP. If the manufacturer has not fulfilled his obligation, you cannot distribute the product. Alternatively, you can become formally a manufacturer. That is a relatively common case, described in this article.
Summary
The obligation to issue a DoP is in place when the product is covered by a harmonised standard or an ETA. Otherwise, a DoP must not be issued. If a DoP is to be issued, the CE marking is also mandatory.