Allah is the guardian of those who believe. He brings them out of the darkness into the light; and (as to) those who disbelieve, their guardians are taghoot who take them out of the light into the darkness
[Surah Baqarah, ayah 257]

From the above ayah it is clear that taghoot is which leads people astray.

All the messengers were ordered to:

‘…Serve Allah and shun taghoot…..’
[Surah Nahl, ayah 36]

From some interpretations people have derived that carrying out legal formalities, accepting conditions or living in a Non Islamic government is obedience to the taghoot. From where have people derived such notions is yet to be known, troubling people to leave the cities and live in the mountains etc is an unwanted restriction they are trying to impose on others.

Yousuf (Alaihi salam) and the Aziz’s kingdom:

Thus did We plan for the sake of Yousuf; it was not (lawful) that he should take his brother under the king’s law.
[Surah Yousuf, ayah 76]

Yousuf (Alaihi salaam) took a post in a government where Allah’s law wasn’t enforced, from this it is clear that to work under a Non-Islamic government isn’t forbidden especially when there isn’t a Khilafah.

Pact of Hudaibiyah:

Prophet Muhammad (SallAllah-u-Alaihi-wa-Sallam) made a pact with the Kafirs of Makkah.

Prophet (SallAllah-u-Alaihi-wa-Sallam) agreed to change ‘Muhammad rasool Allah’ to ‘Muhammad bin Abdullah’ and ‘bismillahir rehmanir raheem’ to ‘bismik Allahumma’ in the text of the pact of Hudaibiyah according to the kafirs ‘s condition.

Ali (RadiAllahu Tala Anho) refused to erase the words ‘Muhammad ur Rasool Allah’, then the Prophet (SallAllah-u-Alaihi-wa-Sallam) himself erased it.

During the writing of the pact, a muslim arrived. The delegate of the kafirs told the Prophet (SallAllah-u-Alaihi-wa-Sallam) to hand him over according to the pact, Prophet Muhammad (SallAllah-u-Alaihi-wa-Sallam) said the text isn’t even complete as yet, but still the kafir insisted, and eventually the muslim was handed over to the Kafirs.
[Sahih Bukhari, Book 50: Number 891, Book 49: Number 862]

Even though they had the power to fight the kafirs still they accepted the kafirs ‘s conditions.

Was the prophet (SallAllah-u-Alaihi-wa-Sallam) obeying the taghoot? Nauzubillah.

Why was all of this done?

It was done keeping in view the overall prosperity that Islam will achieve, from this it is clear that to accept conditions of Kafirs isn’t forbidden especially when today we don’t have Khilafah where we could migrate.

This proves that to acquire legal documents from any government or to accept their conditions isn’t forbidden as Prophet (SallAllah-u-Alaihi-wa-Sallam) made a documented pact with a kafir government and accepted their conditions.

Ibraheem (Alaihi salam) and the Kafir King:

When Ibraheem (Alaihi salam) left his father then he settled with his wife in a place which was ruled by a despotic King. Someone informed the king of the beauty of Sara (rehmatullah Alaihi), the king sent a person for query. Ibraheem (Alaihi salam) told that person that she is his sister in Islam. Then Ibraheem (Alaihi salam) sent her to the king, the king tried to take advantage of her but Allah saved her, then the king sent her back with a slave girl ‘Hajra’, Sara (rehmatullah Alaihi) told her husband that Allah has given us a slave girl.
[Sahih Bukhari: Volume 3, Book 34, Number 420]

Why did Ibraheem (Alaihi salam) sent his wife to the king? Was he helping the taghoot? Nauzubillah min zalik.

Abu Bakr (RadiAllahu Tala Anho) ‘s asylum:

Abu Bakr (RadiAllahu Tala Anho) set out migrating to the land of Ethiopia, and when he reached Bark-al-Ghimad, Ibn Ad-Daghina, the chief of the tribe of Qara, met him and inquired about his travel, Abu Bakr told him that he has been turned out by his people and that he shall wander the earth and worship his lord. Ibn Ad-Daghina after hearing this said that “A man like you cannot leave nor can he be driven out, you can stay here and I will be your protector”. So Abu Bakr returned and Ibn Ad-Daghina accompanied him. The kafirs accepted Ibn Ad-Daghina ‘s asylum for Abu Bakr but with some conditions, Abu Bakr accepted those conditions.
[Sahih Bukhari: Volume 5, Book 58, Number 245]

One of the foremost personalities from among the Sahaba chose to stay in the asylum of a Kafir and that too for practicing Islam, similar is the condition of any person who gets himself registered in any form with any government so that he is allowed to practice Islam peacefully. There is nothing wrong with it, but for those who want to make a mountain out of a molehill.

Kufr can be forgiven:

Even if the above is not enough then the below ayah should also be kept in view.

Any one who, after accepting faith in Allah, does kufr, – except under compulsion, his heart remaining firm in Faith …..
[Surah Nahl, ayah 106]

Allah is so merciful that he is even willing to forgive kufr if we are compelled.

Prophet Muhammad said (SallAllah-u-Alaihi-wa-Sallam):

On my ummah, mistake, oversight and on which they (Muslimeen) are compelled, are forgiven.
[Irwah ul Ghalil lil Albani: Volume 1, 194/8, Hakim, Ibn e Hibban, Sanad: Sahih]

As today there isn’t Khilafah hence a Muslim is compelled to live under various governments, abide by their laws and accept their conditions so that he can practice his Deen peacefully.