However, 128 MB (131,072 KB) is insufficient. Consequently, we can overcome this limitation by dividing our file into smaller parts. This process is relatively straightforward and serves as a common workaround for larger files.

To divide a file into parts, you can use the following code:

static List<byte[]> DivideFile(byte[] data, int chunkSize)
{
    List<byte[]> fileParts = new List<byte[]>();

    int offset = 0;
    while (offset < data.Length)
    {
        int remaining = data.Length - offset;
        int bufferSize = Math.Min(chunkSize, remaining);

        byte[] buffer = new byte[bufferSize];
        Buffer.BlockCopy(data, offset, buffer, 0, bufferSize);

        fileParts.Add(buffer);
        offset += bufferSize;
    }
    return fileParts;
}

When specifying the 'chunkSize' as the part size limit in bytes, it should be set to a value lower than the attachments limit. You can verify this using the following code:

public int GetAttachmentSizeLimit()
        {
            QueryExpression query = new QueryExpression("organization")
            {
                ColumnSet = new ColumnSet("maxuploadfilesize")
            };
            return Service.RetrieveMultiple(query).Entities
                .FirstOrDefault().GetAttributeValue<int>("maxuploadfilesize");
        }

Next, you should save a portion of the data in separate attachments and associate the relevant information. The following details are required:

File information:
Name	Type	Description
FileId	Guid	File identifier
FileTotalParts	int	Total number of parts
Parts information:
Name	Type	Description
FilePartId	Guid	File part identifier
FilePartNumber	int	Part sequence number

Each section should be assigned a sequence number, FilePartNumber, ranging from 0 to the specified value of the corresponding configuration parameter minus 1.

public class FileInfo
{
    public Guid FileId { get; set; }
    public int FileTotalParts { get; set; }
    public List<FilePartInfo> FileParts { get; set; }
}

public class FilePartInfo
{
    public Guid FilePartId { get; set; }
    public int FilePartNumber { get; set; }
}
Example of creating annotations:
List<byte[]> fileParts = DivideFile(data, chunkSize);

Entity fileInfoRecord = new Entity("FileInfoEntity");
fileInfoRecord.Id = _service.Create(fileInfoRecord);

FileInfo fileInfo = new FileInfo()
{
    FileId = fileInfoRecord.Id,
    FileTotalParts = fileParts.Count,
    FileParts = new List<FilePartInfo>()
};

for (int i = 0; i < fileParts.Count; i++)
{
    Entity filePartRecord = new Entity("annotation")
    {
        Attributes =
        {
            { "documentbody", Convert.ToBase64String(fileParts[i]) },
            { "subject", "File subject" },
            { "filename", $"FileName_part{i}.bin" },
            { "objectid", fileInfoRecord.ToEntityReference() },
        }
    };

    filePartRecord.Id = _service.Create(filePartRecord);

    fileInfo.FileParts.Add(
        new FilePartInfo() { FilePartId = filePartRecord.Id, FilePartNumber = i }
    );
}

fileInfoRecord["JSON"] = JsonConvert.SerializeObject(fileInfo);
_service.Update(fileInfoRecord);