Link files lead to new custom object

Question

On Lead conversion I also create a new object to which I map several fields of the lead trough processbuilder. I also want to pass the files from the lead to the new custom object. I am trying to do a query on lead and pass this to the new record Id but I am stuck on linking the content document id which I want to use as a trigger.

See:

List<ContentDocumentLink> ContDocLinksLead = [SELECT ContentDocumentId  FROM ContentDocumentLink WHERE  LinkedEntityId = '00Q1X000001BxVmUAK'];
system.debug('ContDocLinksLead: '+ContDocLinksLead);

ContentDocumentLink LinkList = new ContentDocumentLink();
for(ContentDocumentLink Link: ContDocLinksLead){
    Link.ContentDocumentId = ContDocLinksLead.ContentDocumentId;
    Link.LinkedEntityId = 'a001X000000k7oSQAQ';
    link.ShareType = 'V';
    link.Visibility = 'AllUsers';
    LinkList.add(Link);
}
Insert LinkList;

Answer 1

Your basic principle here is valid, but you've got a number of mistakes in your code that aren't related to ContentDocument management as such. I'll try to help here by annotating your code, rather than rewriting it.

// This is good - to query ContentDocumentLink, you must filter on
// LinkedEntityId or ContentDocumentId. In real use, you'd be querying
// against a Set<Id>, I would assume.
List<ContentDocumentLink> ContDocLinksLead = [
    SELECT ContentDocumentId  
    FROM ContentDocumentLink 
    WHERE LinkedEntityId = '00Q1X000001BxVmUAK'
];   
// The type of this variable is wrong. You want List<ContentDocumentLink>.
ContentDocumentLink LinkList = new ContentDocumentLink();

for(ContentDocumentLink Link: ContDocLinksLead){
    // Here you need to be creating a *new* ContentDocumentLink.
    // ContentDocumentLink newLink = new ContentDocumentLink();
    //
    // ContDocLinksLead is your list variable. You need to be
    // looking at `Link` here.
    Link.ContentDocumentId = ContDocLinksLead.ContentDocumentId;

    // In real code, you'd be mapping between the Id of your original Lead
    // and the Id of the custom object here, to get the new LinkedEntityId.
    Link.LinkedEntityId = 'a001X000000k7oSQAQ';
    // You'll want ShareType 'I' for Files attached to records.
    // This infers access level from the parent record.
    // See https://developer.salesforce.com/docs/atlas.en-us.api.meta/api/sforce_api_objects_contentdocumentlink.htm
    link.ShareType = 'V';
    link.Visibility = 'AllUsers';
    LinkList.add(Link);
}
Insert LinkList;