How to show uploaded php file as plain text instead of executing it in wordpress?

You already have the right code — AddType text/plain php, which will make Apache treats PHP files (or files where the name ends with .php) as plain-text files.

But assuming the following:

• You have WordPress installed in the /var/www/html directory.

• The PHP files are uploaded to the default uploads folder in WordPress (wp-content/uploads).

If you set the directory to /var/www/html/wp-content/uploads as in:

<Directory /var/www/html/wp-content/uploads>  AddType text/plain php</Directory>

You'd get the results you wanted — only PHP files in the uploads folder will be treated as plain-text files, and not all PHP files in the /var/www/html directory. This explains the issue with "To open the post http://home.local/wp/?p=4785, I got the following output", where that output is the code in the file /var/www/html/index.php. I mean, you used <Directory /var/www/html>, which makes Apache treats the index.php file as a plain-text file, instead of executing the PHP code in the file.

ALTERNATE METHOD: Use the .htaccess file.

Particularly if you can't edit or have no access to the Apache's configuration (.conf) file.

1. Create .htaccess in the uploads folder, if it's not already there.

2. Then add AddType text/plain php in that file.

Additional Notes

I want to see the content in testme.php, click it, pop up new window

I'm sure you can do that or already have the code/solution, but an easy way, is just add target="_blank" to the attachment/file link.. or with JavaScript, you can use window.open().

And you must take full security measures since allowing people to upload PHP files could harm your site and/or your site users.

What are you trying to accomplish? It seems you're trying to get a hyperlink that displays the contents of a PHP file. WordPress posts are stored in the database. So when you say "publish it", what are you talking about? The database entry that refers to a WordPress post, or the PHP file? If all you want on the screen is the unexecuted contents of the PHP file, you shouldn't be publishing a WordPress "post". What is contained in the post? If you're talking about putting a PHP file as the CONTENT of a post, that would be a different thing too. Probably the easiest way to display the content of a PHP file is to just rename it to a text file.

myFile.php => myFile.php.txt