Hi there,
opening an exisiting *.docx document containing tab stops and setting the document parameter IsUpdateFields to true will cause Spire.Doc to convert all tab stops into spaces when saving the document.
This bug occurs in Free Spire.Doc for .NET 5.2.12.54041 but seems to be fixed in Spire.Doc for .NET 5.3.46.
Code to reproduce the issue:
var document = new Document();
document.LoadFromFile("bug.docx");
document.IsUpdateFields = true;
document.SaveToFile("bug1.docx");
Bug.docx (rename attachment from zip to docx) is attached to this post.