System.IO.FileInfo fi = null;
try {
  fi = new System.IO.FileInfo(fileName);
}
catch (ArgumentException) { }
catch (System.IO.PathTooLongException) { }
catch (NotSupportedException) { }
if (ReferenceEquals(fi, null)) {
  // file name is not valid
} else {
  // file name is valid... May check for existence by calling fi.Exists.
}

public bool IsPathValidRootedLocal(String pathString) {
    Uri pathUri;
    Boolean isValidUri = Uri.TryCreate(pathString, UriKind.Absolute, out pathUri);
    return isValidUri && pathUri != null && pathUri.IsLoopback;
}

Directory.GetLogicalDrives() // Returns an array of strings like"c:"
Path.GetInvalidFileNameChars() // Returns an array of characters that cannot be used in a file name
Path.GetInvalidPathChars() // Returns an array of characters that cannot be used in a path.

bool IsValidFilename(string testName) {
    string regexString ="[" + Regex.Escape(Path.GetInvalidPathChars()) +"]";
    Regex containsABadCharacter = new Regex(regexString);
    if (containsABadCharacter.IsMatch(testName)) {
        return false;
    }

    // Check for drive
    string pathRoot = Path.GetPathRoot(testName);
    if (Directory.GetLogicalDrives().Contains(pathRoot)) {
        // etc
    }

    // other checks for UNC, drive-path format, etc

    return true;
}

using System;
using System.IO;
//..

public static bool ValidateFilePath(string path, bool RequireDirectory, bool IncludeFileName, bool RequireFileName = false)
{
    if (string.IsNullOrEmpty(path)) { return false; }
    string root = null;
    string directory = null;
    string filename = null;
    try
    {
        // throw ArgumentException - The path parameter contains invalid characters, is empty, or contains only white spaces.
        root = Path.GetPathRoot(path);

        // throw ArgumentException - path contains one or more of the invalid characters defined in GetInvalidPathChars.
        // -or- String.Empty was passed to path.
        directory = Path.GetDirectoryName(path);

        // path contains one or more of the invalid characters defined in GetInvalidPathChars
        if (IncludeFileName) { filename = Path.GetFileName(path); }
    }
    catch (ArgumentException)
    {
        return false;
    }

    // null if path is null, or an empty string if path does not contain root directory information
    if (String.IsNullOrEmpty(root)) { return false; }

    // null if path denotes a root directory or is null. Returns String.Empty if path does not contain directory information
    if (String.IsNullOrEmpty(directory)) { return false; }

    if (RequireFileName)
    {
        // if the last character of path is a directory or volume separator character, this method returns String.Empty
        if (String.IsNullOrEmpty(filename)) { return false; }

        // check for illegal chars in filename
        if (filename.IndexOfAny(Path.GetInvalidFileNameChars()) >= 0) { return false; }
    }
    return true;
}

/// <summary>
/// Validate the Path. If path is relative append the path to the project directory by default.
/// </summary>
/// <param name="path">Path to validate</param>
/// <param name="RelativePath">Relative path</param>
/// <param name="Extension">If want to check for File Path</param>
/// <returns></returns>
private static bool ValidateDllPath(ref string path, string RelativePath ="", string Extension ="") {
    // Check if it contains any Invalid Characters.
    if (path.IndexOfAny(Path.GetInvalidPathChars()) == -1) {
        try {
            // If path is relative take %IGXLROOT% as the base directory
            if (!Path.IsPathRooted(path)) {
                if (string.IsNullOrEmpty(RelativePath)) {
                    // Exceptions handled by Path.GetFullPath
                    // ArgumentException path is a zero-length string, contains only white space, or contains one or more of the invalid characters defined in GetInvalidPathChars. -or- The system could not retrieve the absolute path.
                    //
                    // SecurityException The caller does not have the required permissions.
                    //
                    // ArgumentNullException path is null.
                    //
                    // NotSupportedException path contains a colon (":") that is not part of a volume identifier (for example,"c:").
                    // PathTooLongException The specified path, file name, or both exceed the system-defined maximum length. For example, on Windows-based platforms, paths must be less than 248 characters, and file names must be less than 260 characters.

                    // RelativePath is not passed so we would take the project path
                    path = Path.GetFullPath(RelativePath);

                } else {
                    // Make sure the path is relative to the RelativePath and not our project directory
                    path = Path.Combine(RelativePath, path);
                }
            }

            // Exceptions from FileInfo Constructor:
            //   System.ArgumentNullException:
            //     fileName is null.
            //
            //   System.Security.SecurityException:
            //     The caller does not have the required permission.
            //
            //   System.ArgumentException:
            //     The file name is empty, contains only white spaces, or contains invalid characters.
            //
            //   System.IO.PathTooLongException:
            //     The specified path, file name, or both exceed the system-defined maximum
            //     length. For example, on Windows-based platforms, paths must be less than
            //     248 characters, and file names must be less than 260 characters.
            //
            //   System.NotSupportedException:
            //     fileName contains a colon (:) in the middle of the string.
            FileInfo fileInfo = new FileInfo(path);

            // Exceptions using FileInfo.Length:
            //   System.IO.IOException:
            //     System.IO.FileSystemInfo.Refresh() cannot update the state of the file or
            //     directory.
            //
            //   System.IO.FileNotFoundException:
            //     The file does not exist.-or- The Length property is called for a directory.
            bool throwEx = fileInfo.Length == -1;

            // Exceptions using FileInfo.IsReadOnly:
            //   System.UnauthorizedAccessException:
            //     Access to fileName is denied.
            //     The file described by the current System.IO.FileInfo object is read-only.-or-
            //     This operation is not supported on the current platform.-or- The caller does
            //     not have the required permission.
            throwEx = fileInfo.IsReadOnly;

            if (!string.IsNullOrEmpty(Extension)) {
                // Validate the Extension of the file.
                if (Path.GetExtension(path).Equals(Extension, StringComparison.InvariantCultureIgnoreCase)) {
                    // Trim the Library Path
                    path = path.Trim();
                    return true;
                } else {
                    return false;
                }
            } else {
                return true;

            }
        } catch (ArgumentNullException) {
            //   System.ArgumentNullException:
            //     fileName is null.
        } catch (System.Security.SecurityException) {
            //   System.Security.SecurityException:
            //     The caller does not have the required permission.
        } catch (ArgumentException) {
            //   System.ArgumentException:
            //     The file name is empty, contains only white spaces, or contains invalid characters.
        } catch (UnauthorizedAccessException) {
            //   System.UnauthorizedAccessException:
            //     Access to fileName is denied.
        } catch (PathTooLongException) {
            //   System.IO.PathTooLongException:
            //     The specified path, file name, or both exceed the system-defined maximum
            //     length. For example, on Windows-based platforms, paths must be less than
            //     248 characters, and file names must be less than 260 characters.
        } catch (NotSupportedException) {
            //   System.NotSupportedException:
            //     fileName contains a colon (:) in the middle of the string.
        } catch (FileNotFoundException) {
            // System.FileNotFoundException
            //  The exception that is thrown when an attempt to access a file that does not
            //  exist on disk fails.
        } catch (IOException) {
            //   System.IO.IOException:
            //     An I/O error occurred while opening the file.
        } catch (Exception) {
            // Unknown Exception. Might be due to wrong case or nulll checks.
        }
    } else {
        // Path contains invalid characters
    }
    return false;
}

char[] invalidChars = Path.GetInvalidFileNameChars(); //returns invalid charachters

Path.GetPathRoot(string); // will return the root.

using System;
using System.Linq;
using System.IO;

// ...

var drives = Environment.GetLogicalDrives();
var invalidChars = Regex.Replace(new string(Path.GetInvalidFileNameChars()),"[\\\\/]","");
var drive = drives.FirstOrDefault(d => filePath.StartsWith(d));
if (drive != null) {
    var fileDirPath = filePath.Substring(drive.Length);
    if (0 < fileDirPath.Length) {
        if (fileDirPath.IndexOfAny(invalidChars.ToCharArray()) == -1) {
            if (Path.Combine(drive, fileDirPath) != drive) {
                // path correct and we can proceed
            }
        }
    }
}

System.IO.Path.GetInvalidFileNameChars();
System.IO.Path.GetInvalidPathChars();