Thank you. Is it I mistake to use the present passive as in sentence one?
No. I changed it to "was advised" because sentence #2 used "advised the company". I figured it would be more likely to be something in the past that was being described.
Is it true that if " the" is omitted, we can use the present passive?
Companies/company is/are advised to build an open-design offices to save space and save on running costs like electricity and water.
You can omit the definite article if you open with "Companies are advised" and it will suggest all companies. You can't omit the definite article if talking about one specific company. It has to start "The company is advised to ...".
Note my correction above. You said "an open-design offices". You've mixed the singular and the plural. Choose one - either "... to build open-design offices" or "to build an open-design office".
Also, you didn't put the "is/are" in the logical order. You opened with "Companies" so the first verb you suggested should have been in the plural.
The above sentence implies that company/companies in general are advised to save money on running costs by constructing open design offices as this can lower the running costs. There is no mention of who, or which department or agency, is advising them. Is my understanding correct?
I'm not sure which sentence you're referring to. If you're talking about the third paragraph in post #3, you gave us two possible sentences:
1. Companies are advised to ...
2. Company is advised to ...
I already told you that the second isn't possible without the definite article. However, the rest of your understanding is correct. If you choose not to state who's advising them, then of course the reader doesn't know who's advising them!
I'm going to try to simplify it a bit. Let's forget the whole section about saving electricity and water costs. Here are your options.
Companies are advised to build open-design offices. (All companies and we don't know who's advising them.)
Companies are advised by the planning department to build open-design offices. (All companies and we know who's advising them.)
The company is advised to build open-design offices. (One specific company and we don't who's advising it.)
The company is advised by the planning department to build open-design offices. (One specific company and we know who's advising it.)