After converting a mobi file to pdf, the pdf is gibberish.

[luigi rovatti]

I won't waste time. The conversion log is the following:

Converti libro 1 di 1 (SACRED CORRIDORS: SECRETS BEHIND THE REAL PROJECT BLUE BOOK, WRIGHT-PATTERSON AFB, ROSWELL, BATTELLE, MEMORY METAL, DR. J. ALLEN HYNEK & UFO COVER-UPS)
DeDRM v7.1.0: Trying to decrypt 21v54ni6.mobi
Using Library AlfCrypto DLL/DYLIB/SO
Using Library AlfCrypto DLL/DYLIB/SO
MobiDeDrm v1.0.
Copyright © 2008-2020 The Dark Reverser, Apprentice Harper et al.
Decrypting Mobipocket 4 ebook: SACRED CORRIDORS: SECRETS BEHIND THE REAL PROJECT BLUE BOOK, WRIGHT-PATTERSON AFB, ROSWELL, BATTELLE, MEMORY METAL, DR. J. ALLEN HYNEK & UFO COVER-UPS
Got DSN key from database default_key
Found 6 keys to try after 0.9 seconds
Crypto Type is: 0
This book is not encrypted.
Decryption succeeded after 0.9 seconds
DeDRM v7.1.0: Finished after 0.9 seconds
Failed to initialize plugin: 'C:\\Users\\almark164\\AppData\\Roaming\\calibre\\plugins\\Inept Epub DeDRM.zip'
Conversion options changed from defaults:
  pdf_serif_family: 'MS Shell Dlg 2'
  output_profile: 'kindle'
  cover: 'C:\\Users\\ALMARK~1\\AppData\\Local\\Temp\\calibre_f8og1pb7\\4fz82x2a.jpeg'
  pdf_sans_family: 'MS Shell Dlg 2'
  verbose: 2
  read_metadata_from_opf: 'C:\\Users\\ALMARK~1\\AppData\\Local\\Temp\\calibre_f8og1pb7\\goxw6ffe.opf'
Resolved conversion options
calibre version: 5.12.0
{'asciiize': False,
 'author_sort': None,
 'authors': None,
 'base_font_size': 0.0,
 'book_producer': None,
 'change_justification': 'original',
 'chapter': "//*[((name()='h1' or name()='h2') and re:test(., "
            "'\\s*((chapter|book|section|part)\\s+)|((prolog|prologue|epilogue)(\\s+|$))', "
            "'i')) or @class = 'chapter']",
 'chapter_mark': 'pagebreak',
 'comments': None,
 'cover': 'C:\\Users\\ALMARK~1\\AppData\\Local\\Temp\\calibre_f8og1pb7\\4fz82x2a.jpeg',
 'custom_size': None,
 'debug_pipeline': None,
 'dehyphenate': True,
 'delete_blank_paragraphs': True,
 'disable_font_rescaling': False,
 'duplicate_links_in_toc': False,
 'embed_all_fonts': False,
 'embed_font_family': None,
 'enable_heuristics': False,
 'expand_css': False,
 'extra_css': None,
 'filter_css': '',
 'fix_indents': True,
 'font_size_mapping': None,
 'format_scene_breaks': True,
 'html_unwrap_factor': 0.4,
 'input_encoding': None,
 'input_profile': <calibre.customize.profiles.InputProfile object at 0x0000026C64892A90>,
 'insert_blank_line': False,
 'insert_blank_line_size': 0.5,
 'insert_metadata': False,
 'isbn': None,
 'italicize_common_cases': True,
 'keep_ligatures': False,
 'language': None,
 'level1_toc': None,
 'level2_toc': None,
 'level3_toc': None,
 'line_height': 0.0,
 'linearize_tables': False,
 'margin_bottom': 5.0,
 'margin_left': 5.0,
 'margin_right': 5.0,
 'margin_top': 5.0,
 'markup_chapter_headings': True,
 'max_toc_links': 50,
 'minimum_line_height': 120.0,
 'no_chapters_in_toc': False,
 'no_inline_navbars': False,
 'output_profile': <calibre.customize.profiles.KindleOutput object at 0x0000026C64892F70>,
 'page_breaks_before': "//*[name()='h1' or name()='h2']",
 'paper_size': 'letter',
 'pdf_add_toc': False,
 'pdf_default_font_size': 20,
 'pdf_footer_template': None,
 'pdf_header_template': None,
 'pdf_hyphenate': False,
 'pdf_mark_links': False,
 'pdf_mono_family': 'Courier',
 'pdf_mono_font_size': 16,
 'pdf_odd_even_offset': 0.0,
 'pdf_page_margin_bottom': 72.0,
 'pdf_page_margin_left': 72.0,
 'pdf_page_margin_right': 72.0,
 'pdf_page_margin_top': 72.0,
 'pdf_page_number_map': None,
 'pdf_page_numbers': False,
 'pdf_sans_family': 'MS Shell Dlg 2',
 'pdf_serif_family': 'MS Shell Dlg 2',
 'pdf_standard_font': 'serif',
 'pdf_use_document_margins': False,
 'prefer_metadata_cover': False,
 'preserve_cover_aspect_ratio': False,
 'pretty_print': False,
 'pubdate': None,
 'publisher': None,
 'rating': None,
 'read_metadata_from_opf': 'C:\\Users\\ALMARK~1\\AppData\\Local\\Temp\\calibre_f8og1pb7\\goxw6ffe.opf',
 'remove_fake_margins': True,
 'remove_first_image': False,
 'remove_paragraph_spacing': False,
 'remove_paragraph_spacing_indent_size': 1.5,
 'renumber_headings': True,
 'replace_scene_breaks': '',
 'search_replace': '[]',
 'series': None,
 'series_index': None,
 'smarten_punctuation': False,
 'sr1_replace': None,
 'sr1_search': None,
 'sr2_replace': None,
 'sr2_search': None,
 'sr3_replace': None,
 'sr3_search': None,
 'start_reading_at': None,
 'subset_embedded_fonts': False,
 'tags': None,
 'timestamp': None,
 'title': None,
 'title_sort': None,
 'toc_filter': None,
 'toc_threshold': 6,
 'toc_title': None,
 'transform_css_rules': '[]',
 'uncompressed_pdf': False,
 'unit': 'inch',
 'unsmarten_punctuation': False,
 'unwrap_lines': True,
 'use_auto_toc': False,
 'use_profile_size': False,
 'verbose': 2}
DeDRM v7.1.0: Trying to decrypt 5tgcvgmt.mobi
MobiDeDrm v1.0.
Copyright © 2008-2020 The Dark Reverser, Apprentice Harper et al.
Decrypting Mobipocket 4 ebook: SACRED CORRIDORS: SECRETS BEHIND THE REAL PROJECT BLUE BOOK, WRIGHT-PATTERSON AFB, ROSWELL, BATTELLE, MEMORY METAL, DR. J. ALLEN HYNEK & UFO COVER-UPS
Got DSN key from database default_key
Found 6 keys to try after 0.1 seconds
Crypto Type is: 0
This book is not encrypted.
Decryption succeeded after 0.1 seconds
DeDRM v7.1.0: Finished after 0.1 seconds
InputFormatPlugin: MOBI Input running
on C:\Users\ALMARK~1\AppData\Local\Temp\calibre_f8og1pb7\xtuscss_.mobi
Extracting text...
Adding anchors...
Extracting images...
Cleaning up HTML...
Parsing HTML...
Malformed markup, parsing using html5-parser
Converting style information to CSS...
Creating OPF...
Parsing all content...
Parsing index.html ...
Initial parse failed, using more forgiving parsers
Parsing index.html as HTML
HTML 5 parsing failed, falling back to older parsers
Traceback (most recent call last):
  File "calibre\ebooks\oeb\parse_utils.py", line 211, in parse_html
  File "calibre\utils\xml_parse.py", line 27, in safe_xml_fromstring
  File "src/lxml/etree.pyx", line 3237, in lxml.etree.fromstring
  File "src/lxml/parser.pxi", line 1896, in lxml.etree._parseMemoryDocument
  File "src/lxml/parser.pxi", line 1777, in lxml.etree._parseDoc
  File "src/lxml/parser.pxi", line 1082, in lxml.etree._BaseParser._parseUnicodeDoc
  File "src/lxml/parser.pxi", line 615, in lxml.etree._ParserContext._handleParseResultDoc
  File "src/lxml/parser.pxi", line 725, in lxml.etree._handleParseResult
  File "src/lxml/parser.pxi", line 654, in lxml.etree._raiseParseError
  File "<string>", line 10
lxml.etree.XMLSyntaxError: Attribute _ redefined, line 10, column 244

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "calibre\ebooks\oeb\parse_utils.py", line 218, in parse_html
  File "calibre\utils\xml_parse.py", line 27, in safe_xml_fromstring
  File "src/lxml/etree.pyx", line 3237, in lxml.etree.fromstring
  File "src/lxml/parser.pxi", line 1896, in lxml.etree._parseMemoryDocument
  File "src/lxml/parser.pxi", line 1777, in lxml.etree._parseDoc
  File "src/lxml/parser.pxi", line 1082, in lxml.etree._BaseParser._parseUnicodeDoc
  File "src/lxml/parser.pxi", line 615, in lxml.etree._ParserContext._handleParseResultDoc
  File "src/lxml/parser.pxi", line 725, in lxml.etree._handleParseResult
  File "src/lxml/parser.pxi", line 654, in lxml.etree._raiseParseError
  File "<string>", line 10
lxml.etree.XMLSyntaxError: Attribute _ redefined, line 10, column 244

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "calibre\ebooks\oeb\parse_utils.py", line 224, in parse_html
  File "calibre\ebooks\oeb\parse_utils.py", line 105, in html5_parse
ValueError: HTML 5 parsing resulted in a tree with nesting depth > 100

Forcing index.html into XHTML namespace
Parsing styles.css ...
Generating default TOC from spine...
Merging user specified metadata...
Detecting structure...
Auto generated TOC with 0 entries.
Flattening CSS and remapping font sizes...
Source base font size is 12.00000pt
Removing fake margins...
Cleaning up manifest...
Trimming unused files from manifest...
Trimming 'images/00002.jpg' from manifest
Trimming 'images/00001.jpg' from manifest
Creating PDF Output...
Converting input as a text based book...
Merged 2 instances of ArialMT reducing size from 106.8 KB to 81.3 KB
PDF output written to C:\Users\ALMARK~1\AppData\Local\Temp\calibre_f8og1pb7\3av9w6e1.pdf

Thank you for your patience, let me know what you find.