I think there is now a github repo sample also (https://github.com/Laserfiche/lf-sample-repository-api-dotnet-srv ), haven't tried it yet. But, here is some C# console app code we had used initially for testing, we have a separate implementation that works based on this. Apologize for the crude code, but hope this helps. Just tested quickly now and still works, sorry for all the hard coded paths etc.

using Microsoft.IdentityModel.JsonWebTokens;
using Microsoft.IdentityModel.Tokens;
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;
using RestSharp;
using System;
using System.Collections.Generic;
using System.IO;
using System.Security.Claims;
using System.Security.Cryptography;

namespace ConsoleApp1
{
    static class Program
    {
        static void Main(string[] args)
        {
            Test();
        }

        private static bool Test()
        {
            try
            {

                string repoId = "YourRepoId";
                string entryId = "LaserficheDocIDToRetrieve";
                string clientId = "ClientIDFromDevConsoleAppConfiguration";
                string servicePrincipalKey = "ServicePrincipalKeyFromLaserficheAccountAdminArea";
                string key = System.IO.File.ReadAllText(@"ServiceKey.txt");//ServiceKey downloaded from App Configuration Authentication, placed on same folder as this app
                string uri = $"https://api.laserfiche.com/repository/v2-alpha/Repositories/{repoId}/Entries/{entryId}";
                var token = CreateClientCredentialsAuthorizationJwt(clientId, servicePrincipalKey, new JsonWebKey(key));
                Console.WriteLine(token);
                var apiToken = CreateApiAccessToken(token);
                CreateRepositorySession(apiToken.access_token, repoId);
                EntryInfo resDoc = GetEntryInfo(uri, apiToken.access_token, repoId, entryId);
                GetDoc(apiToken.access_token, repoId, entryId, resDoc);
                ImportDoc(apiToken.access_token, repoId, @"C:\temp\Test.pdf", "LaserficheParentFolderIdToImportTo", "UploadTest.pdf");

            }
            catch (Exception ex)
            {
                string err = ex.Message;
            }
            return true;
        }

        static TokenInfo CreateAccessToken(string customerId, string repoId, string userName, string password, string applicationName)
        {
            TokenInfo token = null;
            var client = new RestClient($"https://api.laserfiche.com/repository/v1-alpha/Repositories/{repoId}/AccessTokens/Create?customerId={customerId}");
            client.Timeout = -1;

            var request = new RestRequest(Method.POST);

            JObject jsonBody = new JObject();
            jsonBody.Add("username", userName);
            jsonBody.Add("password", password);
            jsonBody.Add("applicationName", applicationName);

            request.AddParameter("application/json; charset=utf-8", jsonBody, ParameterType.RequestBody);
            request.RequestFormat = DataFormat.Json;

            try
            {
                IRestResponse response = client.Execute(request);
                Console.WriteLine(response.Content);
                token = JsonConvert.DeserializeObject<TokenInfo>(response.Content);
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }

            return token;
        }

        static AttributesInfo GetAttributes(string token, string repoId)
        {
            AttributesInfo resultVal = null;
            CreateRepositorySession(token, repoId);
            var client = new RestClient($"https://api.laserfiche.com/repository/v1-alpha/Repositories/{repoId}/Attributes");
            client.Timeout = -1;
            var request = new RestRequest(Method.GET);
            request.AddHeader("Authorization", $"Bearer {token}");
            request.RequestFormat = DataFormat.Json;
            try
            {
                IRestResponse response = client.Execute(request);
                Console.WriteLine(response.Content);
                resultVal = JsonConvert.DeserializeObject<AttributesInfo>(response.Content);
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }

            return resultVal;
        }

        static EntryInfo GetEntryInfo(string uriVersion, string apiToken, string repoId, string entryId)
        {
            EntryInfo resultVal = null;
            var client = new RestClient(uriVersion);
            client.Timeout = -1;
            var request = new RestRequest(Method.GET);
            request.AddHeader("Authorization", $"Bearer {apiToken}");
            request.RequestFormat = DataFormat.Json;
            try
            {
                IRestResponse response = client.Execute(request);
                Console.WriteLine(response.Content);
                resultVal = JsonConvert.DeserializeObject<EntryInfo>(response.Content);
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }

            return resultVal;
        }

        static string GetEntryHeaderInfo(string token, string repoId, string entryId)
        {
            string resultVal = "";

            var client = new RestClient($"https://api.laserfiche.com/repository/v2-alpha/Repositories/{repoId}/Entries/{entryId}/Laserfiche.Repository.Document/edoc");
            client.Timeout = -1;
            var request = new RestRequest();
            request.AddHeader("Authorization", $"Bearer {token}");
            request.AddHeader("accept", "*/*");
            try
            {
                var response = client.Head(request);
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }

            return resultVal;
        }

        static void GetDoc(string token, string repoId, string entryId, EntryInfo docInfo)
        {
            
            var client = new RestClient($"https://api.laserfiche.com/repository/v2-alpha/Repositories/{repoId}/Entries/{entryId}/Export?part=Pages&format=Tiff");
            client.Timeout = -1;
            var request = new RestRequest(Method.POST);
            request.AddHeader("accept", "application/json");
            request.AddHeader("Authorization", $"Bearer {token}");
            request.AddHeader("Content-Type", "application/json");
            try
            {
                IRestResponse response = client.Execute(request);
                Console.WriteLine(response.Content);
                ExportInfo exportInfo = JsonConvert.DeserializeObject<ExportInfo>(response.Content);
                var clientDL = new RestClient(exportInfo.value);
                var requestDL = new RestRequest(Method.GET);
                byte[] byteArray = clientDL.DownloadData(requestDL);
                File.WriteAllBytes(@"C:\temp\dl.tif", byteArray);
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }

        }

        static void ImportDoc(string token, string repoId, string uploadFilePath, string parentEntryId, string fileNameTarget)
        {
            byte[] readText = File.ReadAllBytes(uploadFilePath);

            var client = new RestClient($"https://api.laserfiche.com/repository/v2-alpha/Repositories/{repoId}/Entries/{parentEntryId}/Import");
                                          
            client.Timeout = -1;
            var request = new RestRequest(Method.POST);
            request.RequestFormat = DataFormat.Json;
            request.AddHeader("accept", "application/json");
            request.AddHeader("Authorization", $"Bearer {token}");
            request.AddHeader("Content-Type", "multipart/form-data");
            string s = @"{
                  'name': '" + fileNameTarget;
            string s2 = @"',
                  'autoRename': true,
                  'generateText': false,
                  'importAsElectronicDocument': false  
                }";
            request.AddParameter("request", s + s2, ParameterType.RequestBody);
            request.AddFile("file", uploadFilePath, "multipart/form-data");
            try
            {
                IRestResponse response = client.Execute(request);
                Console.WriteLine(response.Content);                
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
        }

        static ApiTokenInfo CreateApiAccessToken(string token)
        {
            ApiTokenInfo apiToken = null;
            var client = new RestClient($"https://signin.laserfiche.com/oauth/token");
            client.Timeout = -1;

            var request = new RestRequest(Method.POST);
            request.AddHeader("Authorization", $"Bearer {token}");
            request.AddHeader("Content-Type", "application/x-www-form-urlencoded");
            request.AddHeader("grant_type", "client_credentials");
            request.AddParameter("application/x-www-form-urlencoded", "grant_type=client_credentials", ParameterType.RequestBody);
            request.RequestFormat = DataFormat.Json;
            try
            {
                IRestResponse response = client.Execute(request);
                Console.WriteLine(response.Content);
                apiToken = JsonConvert.DeserializeObject<ApiTokenInfo>(response.Content);
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
            return apiToken;
        }

        static bool CreateRepositorySession(string apiToken, string repoId)
        {
            bool retVal = false;
            var client = new RestClient($"https://api.laserfiche.com/repository/v2-alpha/Repositories/{repoId}/ServerSession/Create");
            client.Timeout = -1;
            var request = new RestRequest(Method.POST);
            request.AddHeader("Authorization", $"Bearer {apiToken}");
            JObject jsonBody = new JObject();
            request.AddParameter("application/json; charset=utf-8", jsonBody, ParameterType.RequestBody);
            request.RequestFormat = DataFormat.Json;
            try
            {
                IRestResponse response = client.Execute(request);
                Console.WriteLine(response.Content);
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
            return retVal;
        }

        public static string CreateClientCredentialsAuthorizationJwt(string clientId, string clientSecret, JsonWebKey key,
                string audience = "laserfiche.com", DateTime? validTo = null)
        {
            validTo ??= DateTime.UtcNow.AddMinutes(60);
            DateTime notBefore = DateTime.Now;
            var signingCredentials = GetSigningCredentials(key);
            var tokenDescriptor = new SecurityTokenDescriptor
            {
                NotBefore = notBefore,
                Audience = audience,
                Expires = validTo,
                Subject = new ClaimsIdentity(new[]
                {
               new Claim("client_id", clientId),
               new Claim("client_secret", clientSecret),
           }),
                SigningCredentials = signingCredentials
            };

            var v = new JsonWebTokenHandler();
            var s = v.CreateToken(tokenDescriptor);

            return s;
        }

        private static SigningCredentials GetSigningCredentials(JsonWebKey key)
        {
            ECDsaSecurityKey ecDsaSecurityKey = new ECDsaSecurityKey(ECDsa.Create(new ECParameters()
            {
                Curve = ECCurve.NamedCurves.nistP256,
                Q = new ECPoint()
                {
                    X = Base64UrlEncoder.DecodeBytes(key.X),
                    Y = Base64UrlEncoder.DecodeBytes(key.Y)
                },
                D = Base64UrlEncoder.DecodeBytes(key.D)
            }));
            ((SecurityKey)ecDsaSecurityKey).KeyId = key.Kid;
            return new SigningCredentials((SecurityKey)ecDsaSecurityKey, "ES256");
        }
    }

    public class ExportInfo
    {
        public string context;
        public string value;
    }
    public class ApiTokenInfo
    {
        public string access_token;
        public string token_type;
        public int expires_in;
    }
    public class TokenInfo
    {
        public string context;
        public string authToken;
        public DateTime expireTime;
    }
    public class DataElem
    {
        public string key;
        public string value;
    }
    public class AttributesInfo
    {
        public string context;
        public List<DataElem> value;
    }
    public class EntryInfo
    {
        public long id { get; set; }
        public string name { get; set; }
        public long? parentId { get; set; }
        public string fullPath { get; set; }
        public string folderPath { get; set; }
        public string creator { get; set; }
        public string creationTime { get; set; }
        public string lastModifiedTime { get; set; }
        public string entryType { get; set; }
        public string templateName { get; set; }
        public long? templateId { get; set; }
        public List<string> templateFieldNames { get; set; }
        public string volumeName { get; set; }
        public long? rowNumber { get; set; }
        public long? ElecDocumentSize { get; set; }
        public bool? IsElectronicDocument { get; set; }
        public bool? IsRecord { get; set; }
        public string MimeType { get; set; }
        public int? PageCount { get; set; }
        public bool? IsCheckedOut { get; set; }
        public bool? IsUnderVersionControl { get; set; }
    }
}