Europol Public Information Amendments to procurement documents will be provided simultaneously to all operators by the  same means as for the procurement documents. In order to allow economic operators reasonable time in which to take the amendment into  account in preparing their requests to participate/tenders, Europol, at its discretion, may extend  the time limit for receipt of requests to participate/tenders.  Amendments will be regarded as an integral part of the procurement documents.  Except in duly justified cases, candidates/ tenderers who have failed to submit evidence or to  make statements as required in the procurement documents, shall be contacted by the  contracting authority to provide the missing information or clarify supporting documents. The contracting authority may correct obvious clerical errors in the tender after confirmation of  the correction by the tenderer. Such information, clarification or confirmation shall not  substantially change the tender.  Only in the case of a negotiated procedure, if so stated in the Invitation, Europol may negotiate  with tenderers the tenders they have submitted, in order to adapt them to the requirements set  out in the procurement documents and in order to find the most economically advantageous  tender. The minimum requirements defined in the procurement documents are not subject to  negotiation. During negotiations equal treatment of all tenderers will be ensured. Europol  reserves the right not to negotiate and to award the contract on the basis of the tenders initially  received.  The candidates/ tenderers must observe the time limit for receipt of requests to participate/  tenders as specified in the Invitation.  Depending on the type and value of the procurement procedure, requests to participate/tenders  shall be submitted either electronically or as hard-copy via post/courier/hand delivery.  Detailed information about the specific modalities of submission for each procedure is provided  in the Invitation.  Requests to participate/tenders submitted in accordance with the specified rules shall be opened  by Europol in an opening session.  In open procurement procedures, the opening session is public, with the meaning that any  authorised representative of the tenderer may attend the opening session. The Invitation or  Contract Notice will specify whether the opening session is public.  General Guidance on Europol Procurement Procedures  Page  14  of  20 5.2. Opening session  5.1. Submission of requests to participate/tenders  5. Submission of requests to participate/tenders, opening and evaluation  4.3. Contacts with candidates/ tenderers following submission of requests to  participate/tenders 