Why is this PEM file invalid?

I have a file chain.pem that contains two PEM encoded certificates, the first one being the TSA certificate and the second one being the self-signed CA.

the file content is exactly:

-----BEGIN CERTIFICATE-----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vQO6hansgn1gVlkF4i1qWE7ROArhUCgM7jl+mKAS84BGQAeGJEO8B3y5X0Ia8xcS
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khxlliVIBp3Nt9Bt4YHeDpVw1m+HIgzii2KKtVkG8+4MIQ9wUej0hYr4uaktCeRq
8tnLpb/PrRaM32BEkaSwZgOxFMr3Ax8GXn7u+lPFdfNJDAWdLjLdx2rE1MTHEGg7
l/0b5ZG8YQVRhtiPmgORswe2+R7ZVNqjb5rNah4Uqi5K3xdGS1TbGNu2/+MAgCRl
RzcENs5Od7rl3m/g8/nW5/++tGHnlOkvsJUfiq5hpBLM6bIQdGNci+MnrhoPa0pk
brD4RjvGO/hFUwQ10Z6AJRHsn2bDSWlS2L7LabCqTUxB9gUV/n3LuJMZzdpZumrq
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EwQCMAAwHQYDVR0OBBYEFG52C3tOT5zhYMptLOknoqKUs3c3MB8GA1UdIwQYMBaA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-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----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MCAGCSqGSIb3DQEJARYTYnVzaWxlemFzQGdtYWlsLmNvbTESMBAGA1UEBxMJV3Vl
cnpidXJnMQ8wDQYDVQQIEwZCYXllcm4xCzAJBgNVBAYTAkRFggkAwemGFg2o6YAw
MwYDVR0fBCwwKjAooCagJIYiaHR0cDovL3d3dy5mcmVldHNhLm9yZy9yb290X2Nh
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FidodHRwOi8vd3d3LmZyZWV0c2Eub3JnL2ZyZWV0c2FfY3BzLmh0bWwwMgYIKwYB
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CCsGAQUFBwICMDsaOUZyZWVUU0EgdHJ1c3RlZCB0aW1lc3RhbXBpbmcgU29mdHdh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-----END CERTIFICATE-----

If I try to load this using openssl, I get the following error:

$ openssl pkcs7 -inform pem -in chain.pem -text
unable to load PKCS7 object
372716:error:0D0680A8:asn1 encoding routines:asn1_check_tlen:wrong tag:../openssl-1.1.1i/crypto/asn1/tasn_dec.c:1149:
372716:error:0D06C03A:asn1 encoding routines:asn1_d2i_ex_primitive:nested asn1 error:../openssl-1.1.1i/crypto/asn1/tasn_dec.c:713:
372716:error:0D08303A:asn1 encoding routines:asn1_template_noexp_d2i:nested asn1 error:../openssl-1.1.1i/crypto/asn1/tasn_dec.c:646:Field=type, Type=PKCS7
372716:error:0906700D:PEM routines:PEM_ASN1_read_bio:ASN1 lib:../openssl-1.1.1i/crypto/pem/pem_oth.c:33:

I checked answers in this https://stackoverflow.com/questions/45048858/pem-routinespem-read-biobad-end-line one, but It seems the headers and footers are propper - so, what's wrong with this certificate file?

You're using the wrong command

You're using OpenSSL's pkcs7 command. PKCS 7 is a specific format in which to store data. In PEM, PKCS 7 can usually be recognized through the header -----BEGIN PKCS7-----. In Windows, the file format .p7b would be used.

However, those certificates you are presenting are not in the PKCS 7 format, they're PEM-encoded x.509 certificates. As such, the following command will print the correct information:

openssl x509 -in chain.pem -text

It should be noted that this command will only print the first certificate encountered, not both.