Open the word document when calling the COM component of WPS and msoffice

When you call the COM component of WPS and msoffice, you can open the Word document. I want to use WPS and msoffice to convert the office document to a pdf file. there is no problem with excel or ppt, that is, when a word file is opened, the server waits. if a word is opened in a process, you must manually close it. $ Office = open the word document when calling the COM component of WPS and ms office
I want to use WPS and ms office to convert office documents to pdf files. there is no problem with excel and ppt, that is, when the word documents are opened, the server waits, the process that opens the word is added to the process, and you need to manually close it.
$ Office = new COM ('wps. application ');
$ Wps = $ office-> Documents-> Open ("D:/APMServ5.2.6/www/htdocs/pa.doc"); // This is an issue that occurs when you execute this sentence.

WPS and ms office have been tried, and such problems may occur.
Environment: win7 + Apache

------ Solution --------------------
Add one sentence below $ office = new COM ('wps. application ');
$ Office-"Visible = 0;
Try